Honestly I think you can argue that every main is OP.

With enough refines/magatama...

Earth can throw up shields every single round, which stiiiinks.
Lightning paralyzes and does that 10 times in a row thing (*lightning armor) which is reaaaaally annoying.
Water can heal a half-dead team to 100 and clear debuffs with a pretty short cooldown, which ticks me off.
Wind has AOE damage that destroys clone walls, which I really hate.
Fire has ignite/debuff clear/interrupt, which I don't mind since I'm fire XD

And the team has an impact too (I mean, Captain Obvious, but still.)