Well, the current system doesn't really avoid the steam-roll-the-ai-with-capitals problem, but that's not really the issue here, I think.
You can easily get the first 6 capitals with only a modest increase in cost (some thousands credits in total) since you'll build the necessary military research buildings in the early game anyway.
So, in the few games I've played with the new patch against 3 allied hard AIs my first 6 ships were still capital ships, so not really a change there for me.
It gets hard to reach higher amounts of them since you just need so many research buildings, which is very expensive, this forces you to fill your fleets a bit with frigates, which isn't that bad.
The problem imho is, that in large games you could easily build more then 16 capital ships, resource wise, but it would be impossible because of some arbitrary limit.
how about as you research the ability to use more cap ships the number of ships per lvl goes up until the last research which then becomes unlimited.
So, I think this Idea would be a good way to still make it possible to have a lot of capital ships in the late game, but limit it a bit in the early game. The current system isn't that bad, it's just to restrictive in the long end.
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As for the cruiser, for me they are now quite useless. I need too much research buildings for them to get them, so I just never get to use them since the benefits from them are marginal and I'm able to kill the AIs with frigates and capitals just as nice.
Last but not least the AI. It got a bit better, builds now lots of capital ships, which is nice. But it still tries to flee sometimes when there is a jump inhibitor present, making it sitting ducks for bombers.
It attacks strong defenses with small fleets which then get wiped out without any damage to the defense (3 caps, 15 frigates vs. 6 gauss cannons, 2 repair stations, 4 hangars; since the AI attacks the cannons in front which will get repaired very fast it takes high losses without inflicting casualties itself).
It never tries to attack weak targets, it always attacks the same planets, which of course have good defenses from earlier attacks.
The AI leaves its fleet at the edge of the gravity well, so when I attack and jump in, I'm jumping in the mid of its fleet and am able to destroy all it's weak targets (carriers, LRMs, flaks) in seconds since I'm next to them, which weakens it immensely.
The AI seems to be slower in building defenses which makes it easier to overrun and it also doesn't always build repair stations next to it's gauss cannons (a must have for every defense) which still make it weaker.
Btw. nice change to the culture system, I like it how it works now.