I do like the way Mana Leak works now, and so while I think it needs to be toned down I'd prefer that happen in a way that doesn't involve arbitrary limits on which spells it effects (especially when that just gimps the Wizard unnecessarily).
How about: Mana Leak reduces spell costs by -1, but permanently disables MP regeneration (or at least -1 to MP regen, so BLUDTOPOWA will put you at 0 HP/1 MP per tile). It's still powerful, but no longer hilariously broken for regen fighting - and since you'll generally want to save it for late in the game, it encourages staying with Mystera, which makes for an interesting strategic decision since Mystera's piety farmy-ness pulls you just as strongly in the direction of converting out. (I'd also delete the monster magic resistance increase, since that would be nearly impossible to deal with late in the game and Mystera really ought to be the designated BURNDAYRAZ deity.)
That also mitigates the free LEMMISI issue for Wizards, since they'll at least have to deal with the loss of MP regen even if HP regen (or +1 MP regen with BLUDTOPOWA) is still free. Change BICEPS to 3 MP / 45% bonus damage / 3% phys resist reduction, and that issue is solved as well (and I think that's a more balanced glyph anyhow).