Power isn't a factor in Arena. Everything is leveled evenly. The only thing that carries over is Initiative (and maybe something else, but I can't put my finger on it) which is why ninjas that are normally tanky in Sageworld and Matsuri (like Roshi and Red Hot Chili Mama Kushina) are super squish in Arena.

In short, Arena basically takes the Pay to win aspect out of the stats and is reliant on skill. Unfortunately the Pay to Win aspect still lingers in Ninja Availability and Speed.