The 5000+ cross planet attacks etc. sound very scary but actually are not since the AI carriers are so dumb. How it basically has went down for me is they have maybe 2000 troops at large or less, and the rest are in carriers.
But, when I bring my troops on a planet to battle the AI the carriers somehow just wait there and don't try to go after any of my key planets or unload at that planet to assist the battle.
So basically I bring my own 5000 troops to defend against the 2000 AI + 3000 in carriers, and when I've dealt with the "ground troops", I shoot down one carrier, now 5000 my troops vs 1000 AI. I take them down, now there's just a few carriers left which I also take down one by one.
And my losses in that battle will be very marginal because I always overpower their ground troops by at least 2 to 1 but the losses for AI are huge.
Is this how it goes down with everybody else too?