Bardiche: You heard the discussion, but just to summarize for everyone else: Ether skills, if allowed, would be a net boost to his damage, though not a colossal one (notable, mind). Maya's HP is only that low if you don't allow stat customization and just run with OK's numbers (P2:IS Maya build, which is low Vit). She can easily score gamebest HP/near best defense, have gamebest Tec, and -nearly catch up to Ulala in Agi- at level 65 (this puts no points in Str which she never really wants in game and she's fucked if she's relying on it for the DL, and Luc which doesn't affect enough from my tests to make it something she wants to invest into DL-wise.)
Defense stat is potent, definitely notable, though I can't give you a x defense/y damage conversion yet, sadly. She flat halves damage of all sorts with Dance of Protection up.
My calc of Vayne's damage is 1.7x PCHP with a full rush by your method (very good, I'd not have noticed that possibility). Going by flat numbers as they stand in both topics, one more thing Maya has - she can equip for evasion. About 10-20%, but that should shave enough off each attack that she can survive the rush, barely.