They are broken in at least two ways:

1. The AI seem to be able to assimilate them even when there's no way it's had any contacts with them. 

On this screenshot you can see the Poles (purple) who spawned on the continent on the right (upper right corner) yet, as early as the classical era, they somehow managed to assimilate two independent people on my main continent (I'm playing Green).

This first point isn't too bad when it happens on your main continent, but it doesn't seem logical and, as a result, the two other AI on that continent were denied some potential territory which might have made them a little more competitive (and interesting).

However, this issue also happens on "New World" continents and that's where it becomes stupidly game breaking.

In that case, it means you don't need to compete for the caravel technology when you can just assimilate some independent people and gain a big city with lots of troops to colonize the new world.

Doing that, as a player, removes a huge part of the fun and challenge of exploring the new continent and rushing to get there first. Not doing that means the AI might get there first.

A very simple solution would be to allow assimilation of independent people only if you already have a city on their continent and/or if you have the appropriate seafaring technology.

2. The assimilation mechanic seems bugged

At least it seems bugged to me but I might just have missed something: 

On the screenshot above, we're at turn 128, the Poles (again) are apparently about to assimilate those people who are located on the new world. however, that's not really what happens:

In fact, on the next turn they are suddenly, without any warning, assimilated by the English who, somehow went from not competing for them at all to total assimilation in just one turn.

I'm not sure what happened here but regardless of that issue, the main point is that assimilating people on the new continent when you still don't have ocean crossing tech is just game breaking.  

One of the pre-built AI has a trait that basically gives them +rep with all of the independent nations on the map without them having ever needed to meet them or spend anything. It's broken and needs to be fixed so that it only affects nations that they've met.

Honestly, I'm not a huge fan of the trait system in general. Players don't have access to it for their own strategies and a lot of them are over-tuned. I know they did it to try to make the NPCs more distinct and unique, but it's just not very good.

SpicyCrab wrote:

Zevkk wrote:

Honestly, I'm not a huge fan of the trait system in general. Players don't have access to it for their own strategies and a lot of them are over-tuned. I know they did it to try to make the NPCs more distinct and unique, but it's just not very good.

Those are just cheats for AI that you can actually see because, you know, AI can't compare to a human player. So the game has to compensate for it just like most 4X games if not all.

Yeah, but it already does that by providing FIMSI boosts and combat strength bonuses on the difficulty you select.

Apparently, some Redditors did some testing on this and it's not actually tied to the AI trait, but rather just that any AI in the 3rd slot will get the +rep with all independent cities for free. The only work around is to use a persona with the 'Metropolis' trait in that slot. Otherwise, it's a bug that you just have to deal with until it's patched.