I'd recommend to try my weapon balance mod on a campaign. You can make quite good hybrid designs there, because all beams or all missiles design are not the best designs anymore. If you want to have strong middleranges ship, you can through hybrid designs like 1x Kinetics / 1x Missiles / 1x Shield.

I have no sense of what's going on, or how best to build for a particular strategy.  I certainly win more than I lose, but I feel like I'm guessing at how things work.  I do definitely think it's a step up from the previous iteration (there's meaningful choices now), but I felt like I had a greater sense of control in ES1, and that there could be surprises. 

ES1 had "rocks scissors paper" atop "rock scissors paper," but in a way that created a need to read your opponent.  Fleets of missile destroyers, for example, could destroy your enemy before he could deal any damage to you, so you needed little armor (the "iajutsu" strategy, or glass artillery).  The counter to this is, first of all, that flak was superior, pound for pound, to any defense.  Beam weapons also hit sooner, so a beam-weapon focused fleet could hit missiles just before missiles hit artillery, albeit with inferior accuracy, but there were strategies that could overcome this.  Together, both of these made ballistics the worst... unless you could armor up and get close, in which case you had the "juggernaut" strategy, which I found worked very well with the Sheredyn as they could prevent their enemy from fleeing if their initial salvo didn't take them out.  Which brings us to our cards: Once you understood the design metagame, you could try to outguess your opponent with cards, based on how your ships were built and how his were.  And, of course, extremely advanced heroes made a huge difference in your strategy options.

In ES2, I have no real sense of how combat works.  I've been learning a bit more, but it seems even more solidly in favor of long ranges than short, because you can elect to keep your distance.  There is the possibility of making better use of "mixed arms" in that you can have close-range ships sweeping in close while long range ships pound from a distance, but I've not really found that I make much use of this.  There also seems to be arcs of fire (frontal and broadsides, perhaps?) but this also seems difficult to take advantage of. In practice, I tend to pick ballistics or energy based on what my civilization is good at, and then I just churn out enough ships to overwhelm my opponent.  I rarely really care about what specific tactics I use, and I tend to pay more attention to keeping my distance from my enemy, or at least keeping my opponent from reaching optimum range, though in practice, despite the presence of 3 ranges, there seems to be only really two: Long-Medium, and Short, as most things that are good at hitting you at long range are also good at hitting you at medium, while things that are good at hitting you at close range suck at hitting you at both medium or long (the degree to which this is true varies)

We also don't have that many tactics.  I know we can change our decks, but I usually only do this once a game, when I get a new set of cards.  There doesn't seem to be a lot of play/counterplay, in that I guess, see what my opponent does, and then try to respond to either drive home an advantage or rally to try to salvage the situation, or flee now that I know things have gone sideways.  I like that you have to pick and choose what tactics you develop, but I don't have any further sense of personalization.

Heroes don't do much the sway battles except in that they're a free ship in the battle, and you can upgrade it.  Experience is excruciatingly slow for heroes-as-admirals, and their biggest benefit, other than that free ship, is that they improve movement speed (thus I'm a big fan of seekers).  Beyond that, I generally find Heroes, especially late game, are far better off as governors than heroes.

There are three deployment vectors, but I don't know how to control those or implement them.  They just happen. If I have a close-range beam ship and a long-range missile ship in a fleet, I always just get one attack vector. I can't try to make the beam-ship close and the missile-ship go long.  If I have enough ships, whatever that number is, then they'll split up, but unless you really know what those break points are (and I don't) you'll always get some ships in the wrong vector.  The result is that I don't care about them.  Things just happen, it's a mess, I have no control, so I typically just focus on a single design and max it out.

The Fleet benefits, like giving a ship something like +25% fleet damage, evidently don't stack, so I'm generally best off with one of those in my fleet, and the rest as combat craft.  Speaking of which, the only thing worth spending any resources on are those fleet bonuses and perhaps engine speed.  The current weapons and armor bonuses from strategics are always eclipsed by generic weapons and armor currently.

Finally, I had no idea what experience does.  I presume it makes my ships better, but I see no statistic increases.

So, I lack feedback on what's going on, I have no knowledge of fiddly bits that are buried under the system, and even if I had, I feel like I lack control.  What works best isn't the fiddly bits, but overwhelming them with generic design and superior fleet size.  Don't invest a hero on a fleet, don't give your fleets character, don't worry about your tactical choices, just pick between beam weapons or missiles, go for medium/long range cards that give an okay bonus, then use that combination over and over again while overwhelming your opponent with superior industry and technology, because tactical choices don't really matter that much.

Endless Legend and Endless Space 1 both had much more involved tactical options than his.  ES2 is prettier, I will give it that.

Personally, were it up to me, I would either simplify it further (long/short rather than long/medium/short, and remove ship design options, as there's usually a "best" configuration per faction type anyway, ie Vodyani should choose beams and Cravers should pick missiles, and just unlock ship options based on unlocked hull types and weapon advancement levels), or I would complicate it further.  Give us more control or stop making us fuss over stuff that doesn't matter.  Right now, ES2 has sort of "worst of both worlds," in my opinion.

I only ever used the "Power to shields" card and won most of my battles without a scratch.

there definitely should be more drawbacks / advantages to consider, but it would also be nice if the game offered more help as to how the battle actually works, because despite winning them this easily I still have no clue.