Big ol' wall of text coming. Apologies. I've bold highlighted the section areas.
 
I've had a few playthroughs as Lumeris recently and I don't think I'm alone in putting them in as one of the weakest factions (if not the weakest) right now. Just to caveat, I don't think the game ever can be 'completely balanced' but it does feel like a shame to leave some factions in the dust (no pun intended) compared to others. Also, it's quite possible I'm just missing something with Lumeris gameplay, but I have enough hours in the game and enough playthroughs to feel confident in the critique. So I'm going to look over their unique abilities, their strengths, and weaknesses, and make some suggestions as to small tweaks to improve their playstyle.

Let's start with analysing strengths and uniques:

1. Early game: Lumeris have three things going for them in the first 40 turns.

The first is that they are incredibly good at exploring. The extra probes are great , and with two scouts and your hero you can cover a lot of the map fast. This means you get to pick up lots of extra science, dust, population exiles, and resources to use/sell early. Cool.

The second is their colonisation ability. Not spending industry on colonisers is great, but the real bonus comes being able to colonise without using food if you settle on 'probe scouted' systems outside of your constellation. Food ships will only be sent out if you have warp, which you probably won't this early, or might want to delay for a bit.

The third and perhaps the best is the ability to very quickly gain status with minor factions. As you us dust not influence (which you produce less of), and the first pacifist law reduces the cost of bribes, it is very easy to have a few minor factions fuelling an extreme science and dust economy for the first stages of the game. Lumeris can blitz through the early game powered by minors.

Problems: All of these are specifically early game strengths/are very map dependent and very quickly fall off in the mid game.

For exploration - there is only so much map to explore. Yes, there will be curiousities popping up from tech advancement, but nothing compared to the start.

For colonisation: You will want warp, and you'll want it fairly quickly depending on the map. Here's the kicker - the maps where you want faster warp are the maps you'll be able to get the most out of this ability. To explain - a twin galaxy map doesn't need warp so quickly, as there are only three constellations. But as there are only three constellations, you can't really use your colonisation ability to full effect. Conversely, a spiral 8 might have five constellations, which means you can get a lot out of colonising scouted systems, but also means you're going to want warp faster, negating the advantage. The ability is still an early game advantage, and might save you some food and turns here and there, but it's a small advantage, and one that wanes quickly when the early colonisation period is over.

For minor factions: The boost is incredible at the start and needs to be used to full effect just to be competitive, but as turns reach the 50's the AI's will start conquering or overtaking you as suzerain for the minors (at least on Endless they will), which means you need to take those systems yourself. Fine, but now you're just in the same boat as everyone else economically with no real advantage.

2. Trade: Lumeris get one extra trading company. A little dull, but still an advantage.

Problems: Trade is rubbish. It needed a nerf for sure from what it used to be, but even a well established, very long trade route will net you around 2-3k dust, a few hundred science, and a pittance of extra resources. This is with every trade boosting building available. Furthermore, AI's don't seem to prioritise trade at all. You can give them the tech and they still won't build many trade companies for a while. That means no external subsidiaries for a while, but even these don't add a whole lot of value. Basically trade companies are a nice way to keep a good dust income, but not one that can win you an economic victory in a timely manner, nor one that is particularly worth the industry (for the companies, and trade boost buildings) and dust investment.

It's still an advantage the Lumeris have, but it's so marginal it's barely worth considering an advantage. Unless it's required by a quest, I often don't bother with trade routes anymore. Having a +dust income is usually enough.

3. Planet Brokers: I have an idea what was trying to be achieved with this skill. For example, there is nothing stopping you from selling off a system for a load of techs, then immediately declaring war and retaking the system. Or just swapping systems for better trade routes.

Problems: There is no way the AI would ever do the latter, and the former really is a niche use. Other than that, I don't really know why this ability exists any more. Does anyone use it, and have I just missed something?

Ok, that's the "strengths" covered.

Now the clear and specific weaknesses:

1. No industry+: The Lumeris have one, just one, way of boosting their industry, which comes from certain quest choices, and it's an industrialist law that gives you 25% on ecstatic. Great... So to use it, you need to keep industrialists in the senate (even though you're pacifist), keep at ecstatic, and even then get very little out of it because your base industry is so low.

Let's compare to some other factions: Sophons extra industry on cold with their XII replacement, plus the first science law which is near OP. UE, Design School from quest, easy to access industrialist laws that give some pretty great industry bonuses, and influence buyout. Riftborn, great pop, happy on lava, singularities. Horatio, splicing and quest industry buildings. Vodyani, Ark modules.  

This problem would be fine if for two things. First, if a buyout economy was possible, but due to inflation, it isn't. You might be able to rush some stuff occasionally, but dust will never replace industry as it stands (unlike say, Endless Legend, where a buyout economy is legit). Second...

2. No science+: Low industry is sometimes ok if you have science to get to high tier +industry buildings a bit earlier to make up the deficit. This should be the role played by the extra trade bonuses, but the science bonuses you get from trade are abysmal. The extra trade route will be lucky to net you more than 500+ extra science, which is pitifully low and only comes after some hefty investment. Other than that, Lumeris get no science bonuses, which I'm pretty sure makes them faction unique. Everyone else gets some form of bonus to science.

These problems are major, and industry and science are the most important resources in the game, but maybe it could be resolved if it wasn't for a third clear problem:

3. No influence+: With some good influence production you can run laws that offset some of your weaknesses, but also importantly negotiate (often with poor deals) techs with AIs that allow you to stay on the curve, if not ahead. Unfallen, for example, have some very similar problems, but can often negotiate their way out of science deficits due to some big influence bonuses from their Guardians and heroes.

Those are the specifics covered. The general problem for Lumeris can, I think, be summed up with the following concept: "Low Dust Utility". Just to explain what I mean:

Resources for any game, but particularly 4X can be thought of in terms of a utility value, or how useful that resource is, often in terms of generating other resources. For example "industry" has a very high utility, if not the highest, as it allows you to generate lots of every single other resource in the game, from ships, to science. You want lots of industry, because there is a lot you can do with that industry. Science also has a high utility, as it allows you to get lots of all the other resources in the game (by researching the techs).

Faction design around a particular resource (Sophons - science, UE, to influence) often falls under two patterns (or a mix of the two):
 1. Allowing the faction to get more of a high utility resource compared to other factions e.g. Sophons get more science.
 2. Giving a resource more utility for that faction e.g. UE can buyout with influence increasing the utility of influence, Horatio produced influence from food, increasing the utility of food.

(Not all factions are designed around a resource, but around a more advanced mechanic - Hissho with behemoths for example, or Cravers with population management/depletion. This is one of the things that makes the Endless games so wonderful)

Lumeris fall *mostly* into the first camp - they have the ability to produce a resource in much greater amounts than others. The problem is, that resource - dust - is not a high utility resource in ES2. Dust does allow you to get all the other resources in the game, but not very much of them, nor at a good rate compared to other resources. For example, dust technically gets you more science through trade route investment, but it doesn't make you very much. It also technically gets you industry, but again, not very much due to prohibitive buyout costs from inflation. Dust does have a little more utility for Lumeris. They get slight buyout reduction bonuses (from Workers Campus - an extra 10%, wow!), and, of course, they use it for some of the early game stuff mentioned earlier.

To be clear, it's not the case that in theory dust couldn't be a high utility resource. The problem isn't that it can't produce the other resources. It's that it doesn't produce enough of them to be worth the production in the current state of the game. 

In terms of improving the Lumeris then, there are two options here. The first press on with their current design, but allow them to make even more dust to make up the deficit of low dust utility. This has one major problem - economic victory. To make up the difference between the low utility and dust production, would mean giving the Lumeris so much dust production that economic victory would become too easy. This used to be the problem with trade routes and the low EV threshold. I take it we don't want to go back to that.

So instead, how about giving Lumeris something that increases their dust utility a little more. I can think of two ways of doing this, that I don't think would radically change how Lumeris currently are, but would give them an extra boost.

First would be to add another unique buyout reduction bonus to an earlier dust producing building. Xeno tourism would be a good bet on this one. A 15% buyout reduction would be sufficient. With Workers Campus, this would be a total unique reduction of 25%, which is not unreasonable, would offset inflation, and would allow for a decent buyout economy which overcomes the industry woes of the faction.

Second, (and I'm not sure a second one is needed) slightly increase the science and luxury resource gains from trade routes. This goes some way in sorting the mid game science issues Lumeris run into, and in general I think trade routes could just do with a small buff to make dust a more important resource in the game in general.

Those are my thoughts but I'm open to criticism/other thoughts for improvements elsewhere. One thing I will pre-emptively argue, as I know it's a bit of a hot issue, is about inflation. I think the inflation mechanic is fine. I think the problem with inflation is the inability for dust orientated empires (like Lumeris) to counteract it. Limiting other empires ability to utilise buyout by increasing your income is honestly great, but it shouldn't come at such a big cost to yourself. So more reduce buyout buildings for Lumeris would effectively resolve the problem.

If you made it this far, thanks for reading.

This is right. Lumeris' main resource was suppossed to be the Dust but it will be devalued by the efforts to get it more. At least for Lumeris, there should be some measures to hedge the losses from Dust inflation. At the same time, as the economic victory threshold does not change, Lumeris is not allowed to have too much Dust production bonuses.

What about giving a refund on an outpost at inflated price? If Lumeris choose to get a refund upon the completion of outpost growth, pay them back with inflation-adjusted amounts of Dust. In this way, Lumeris can hedge the inflation but they will not get any more bonuses on economic victory.

Hey imma gonna necro this cause it's still up to date.

My issue here is, everyone can sell resources and do buyouts.

EVERYONE.

Who needs to spend 3k one expansion or minors? Lumeris.

Who can spend 3k on 10 cp fleet of weapon heavy scouts (or colonizer perhaps) EVERYONE ELSE.

From MP perspective, when you knocking on someone's door as early as turn 10, having a bank of dust and having had spent that bank of dust on things cause you are Lumeris is difference between life and death.