Mindhunt I think is generally speaking not going to be a huge problem. Sure, it's not gonna be the funnest thing in the world if you go up against a nation really optimizing mind hunt spam (regardless of the nation you're playing), but if you're expecting it you can do things to compensate to a fair degree. Just one or two specters (which your pretender can fairly easily summon along with llamia queens) boosted up to S3 can teleport and are stealthy so your opponent never knows where they are or even how many you have - only that the really tempting targets tend to feeblemind his guys more often than never. Add to that swarms and swarms of black harpy decoys that he never knows how many are where - or better yet Centaur Heirophants with 15 base MR who you can stick lead shields & armor of souls on, plus MR amulets if you've lined up lizards or sages or whatever. It starts looking a lot harder to just snipe the guys you want even if they do have low MR. How many mind hunts can you really expect to drop turn after turn with no clams? I think they'll often run out of pearls before you run out of harpies even if you don't have any astral cover, and those feebleminds really start to hurt with any S cover at all. In addition, if you're going up against somebody likely to blast you with mind hunts - there's no reason at all that you can't leave most of your combat Pans untransformed, or use the ones that happened to transform into something with a decent MR (there are some). You can use domes to protect the research centers if mind hunts start poaching there and you haven't lined up any S inies at all - mind hunts aren't the type of thing that suddenly drop 20 at a time so you'll have time to respond before too much damage is done. All in all, I think that threat goes into the "pain to deal with" category rather than "OMG, WHAT AM I GOING TO DO?"
As to battlefield stuff, I think you're underestimating how resilient some of these suggestions are. Wrathful Skies? Super harpies & iron bane will kill them before it bites. They add storm? Hasted centaurs go across the battlefield almost as fast, and eventually you've got fairy queens or Gaia's blessing which means their regen lets them mostly ignore the damage. Master Enslave? Oh, sorry, I'm leading a bunch of mindless dark vines and this year's fashion is all about armor of souls to boost my blood magic and lead shields as accessories. Better luck next year... The white centaurs do *only* have a 14 MR, I guess they'd be the weak spot - unless you're counting the cave drakes thrown in mostly to sucker your enemy into going with MR counter stuff.
What astral specifically are you thinking is going to pose a problem?