[Micah]

I'm playing Rlyeh now, and their late game is pretty ridiculous, and their research to get there is blindingly fast, with 8-RP recruit-anywhere mages.

Their astral magic IS significantly different from other astral races, in that EVERY ONE of their mages can cast teleport out of the box, not just the cap-only ones. What that means is that you can expect a steady stream of magic-dueling suicide bombers aimed at any mages you have in your army to counter their mind hunting or get off that vital antimagic cast against them. Other astral races can't really afford to be so callous about tossing their S4 mages at you to die, since they generally get 1/turn with a lucky random, tops. Other than that, yes, their astral spell list is the same, and having high MR will give them fits. (Marverni has S2 and 2 randoms on non-caps, so they could get multiple S3-4's per turn, but they're 100 more gold each, 1 less base astral, and Marverni isn't known for making it to the late-game...I think they're the only shot at multiples S3 without 10% random picks though)

That being said, rlyeh's early expansion is fairly slow, and their mid-game kind of sucks, I lost a couple of battles with Pan where I had 8 times the gold value of his troops on the field...Pan is a particularly bad matchup due to high innate MR, but still, I got destroyed. Illithid mind-blast artillery is too expensive for how effective it is in most cases, and lobos suck at anything except being damage sponges. Other ground troops are either 30 resources (on a sloth-3 nation) or have 8 morale, so pre-nether darts rlyeh's ability to inflict damage on a large army is sorely lacking, since their mages have weak or single-target spells, and their troops are either horribly overpriced or fairly ineffective. (Crab hybrids being the exception, but they're aquatics)

So, to beat them, expand faster than them, keep them off the land as much as you possibly can, and hope that you have enough of an income advantage to beat them in the war of attrition that will occur late-game, since teleporting everywhere does get costly. Raid the hell out of anything you can with either a stack of commanders and scouts with some chaff (make them burn 10 mind hunts to stop you), or else a single commander with good base MR, a lead shield, a skullcap, and an antimagic amulet. Or pray you find stealthy astral mages, or empower some scouts, just a few cut cords will probably put a bad taste in their mouth. And recruit lots and lots of cheap astral mages if you can, so you can try to keep your important ones alive.