As long as your ships are faster, all you have to do to defend against a much more powerful ai, is dodge their fighters, then swoop in and kill the troop transports...
after this happens 2 or 3 times, they should really move their fighters and troop transports onto the same tile, and bring them in together... but they dont.
This is on tough/intelligent. I was lead to believe ai behavior is the same beyond that difficulty.
Fix it