Stacking STR isn't effective anywhere anymore, Abyssea or not. Non Verethragna 90 MNK (assuming a base STR of 82+5 from merits) will need 4 less STR to cap fSTR, which means 109 VIT on the mob. 90 Spharai MNKs will need 4 more, so 101 VIT on the mob. A level 90 monster with A rank VIT in type, job, and subjob will still only have 93 VIT (this type of mob doesn't even exist and I think Vrtra/Tiamat/Jorm are the only non Abyssea mobs higher than 90 anyways.) Yeah, stuff like that simply just doesn't exist.