Which jobs is at its prime?

[Mhaeric]

I honestly dont think that any other class (could be wrong here) has skills that actually punish you for using them.

Dark Knight has The Blackest Night which punishes you if not used correctly. Unlike MNK abilities, however, the reward is strong enough, the penalty is relatively minor, and the player skill needed to avoid the penalty is not high. It's proof that this type of risk vs. reward skill can work well. MNK skills like Tornado Kick don't check any of those boxes, however, so fail as a risk-reward concept.