The Cruel AIs do cheat when it comes to resources and credits and I think maybe on research. Not sure on the research one.
Thing is thats the only difference when it comes to the other difficulties except they maybe move a bit faster in terms of decisions. Just set up a fully upgraded SB at a major choke point with repair bays, phase jump inhibitor, and station your fleet there and you really are good when it comes to defense. From there you can just tank all their attacks and possibly farm quite a bit of exp for your capitals.
AIs always have the tendency to just suicide on your SBs. This isn't online where we would actually just go around.
Heck you can do 9 Cruels vs 1 with this. IF you pour enough research to defense in armor/shield upgrades as well as give a few weapons upgrades.