I think I can confirm with the unfair AI, it usually sends few capital ships (often lvl1) + fleet against my fully upgraded starbases (let's say neutral grav well, so there's just the starbase), once they hit the research also with some anti-structure ships but they go down quick to those 10/14 fighters stationed on the starbase (and the starbase itself).
After the 6/7th attempt they are almost about to bring it down (since repairs are not much quick) but..whops..my capitals appear in the gravity well, vanquish the poor offenders and repair the starbase, rinse and repeat.
Even on large maps, after they lose lvl 9 capitals this way they keep doing it (with newly built lvl1) regardless of the fact that they're just providing free experience to the enemy while losing their best units and that is costing the match.
They lose territory since they're not able to defend it after the above and the rest comes alone, they can't advance in research anymore and the already unlocked fleet cap turn them to street robbers while you don't know where to spend the resources anymore.
Generally I've noticed too that the AI isn't able to properly evaluate the danger, they just pick what they have and launch it against the enemy in suicide.
Also, apparently they don't know how to properly use a bunch of repair stations backing a defensive fleet and they never built a mass destruction weapon against me (large maps or not), never, I play Sins from when it reached the shops.