480 MP is 1/5 of a Dark Arts use. It's also the amount of MP restored by a tick of Blood Weapon, and 4x the amount of MP restored by Blood Price. In short, it's not free. Likewise, Tomahawk costs the same amount of TP as Overpower, and Shield Lob and Shield Bash cost double the amount of TP as Total Eclipse. So this infinite supply of axes and shields that you can throw from range isn't free, either.

I think it's a similar question to whether Scathe should be free on BLM. You're taking a potency loss anyways for using it. But there's a psychological effect there as well. You're not supposed to feel good about moving on a caster. Likewise, you're not supposed to feel comfortable moving off the boss on a tank or melee. You might see players toss out one or two Tomahawks when they're doing a mechanic off the boss, but they certainly aren't going to burn their TP dry before they get back.

Either way, I don't think we can easily predict what's going to happen without more information. I think WAR would benefit from operating on a single resource system and not using MP at all, but I could see PLD following a similar route to DRK, given that it already uses a two resource system.