Zout: the "don't send wave" AI types at higher levels are actually probably more difficult than the send wave types. Consider that every so often the AI will send a massive pile of junk at you, but there are ways to learn how to manage that, with AI wave senders. With non-wave senders, that massive pile of junk that would otherwise be sent at you is sent to reinforce the planets around you, making expansion extremely difficult after not too long, and making any offensive action very dangerous because of the possibility of releasing ridiculous piles of threat.
Red: I don't think the hardest AIs really cause too much of an undue problem for some of them. Golemites, for instance, have golems on some of their planets sure, but otherwise they function normally. Just treat golems like mobile fortresses. Attritioners have attrition emitters, sure, but those are both easily destroyed (transport with 20 bombers or so, boom!) and capturable. Scorched Earth is a nightmare any way you look at it, Everything is hilarious (though scary!). Just set your randoms to "Random Non-Technologist" and have some fun, you'll get used to it eventually.