Buffs are extremely important in Arena. Considering base stats are lowered and the only statline that Arena takes is initiative.
Also considering how Defense/Res aren't scaled up with equipment/Runes/8 Gates, etc, Damage (Just like how it was in the early levels) outshines in Arena. Healing scales with Ninjutsu, the base numbers don't provide a "great" value, so it seems lackluster.
Unfortunately, that's how it is when it comes to arena.
Hopefully, that helps.