That Darkside adjustment makes me think they don't realize the problem... It's the same issue Ninja has with Hide; You can be fairly far away from the action, but the game still counts you as in combat, so you can't use Hide, or in Darksides case, it keeps draining MP. That's assuming they're not just reducing the initial cost of it by 1/3... I've never found the cost a problem though, it's always been the fact that it drains MP when I'm not actually in combat.
Honestly, just give Paladin and Dark Knight Mana Draw... If it can be justified on Bard and Machinist, it can be justified on Paladin and Dark Knight...