There's nothing wrong with having a cooperation-based MMA.

Don't think Steel Devil should be that MA, though. I had the distinct "lone swordsman facing off against entire squads" vibe from the flavor text.

Definitely don't think "your mainstay attack Charm is useless unless your chums soften the enemy up a bit" is a good cooperative mechanic for any MA. There are better ways to emphasize teamwork mechanically.