It will probably play in favor for MNKs specially where counterstance ruins our defense. I'm inclined to think that it would make mages mobs/players alike more prone to taking higher critical damage than they do now, while jobs like PLD MNK and WAR would take obviously less than they currently do.

Then again the update might only make it noticeable on things that significantly higher VIT, like NM's to hurt peoples abilities to solo stuff as easily in Abyssea.

Course there is the panic button theory that it's going to overall reduce Crit. Damage and ruin jobs like MNK THF NIN and DNC.