The combination of AI ships into higher-level ships has nothing to do with strategy, and everything to do with keeping the unit counts lower so that lower-end CPUs can handle the game. So if you see one Mark IV bomber attacking you, and I was to turn off the combination, that would then be 4 Mark II bombers or 8 Mark I bombers. I think that would be just as difficult to defend against, if not more, just not as unsettling.
I think the real problem here is this: since turtles reinforce only, that means they are also getting tons of special forces ships, which they are then using on the attack against you. There is an imbalance on how the turtles get reinforcements, and I am starting to think they might should get no special forces reinforcements (or very few of them) in general. I think those two things (the former of which is already on my list), are the two real issues that need to be fixed here for now. The rest is just secondary effects of these primary issues, I think.
Thanks for reporting it, again!