Initiative is not the only factor that affects Arena. Ninja buffs contribute to a very large part of the damage. There are multiple ninjas players c*e without needing to spend too much. Ninjas like Regular Gaara and Regular Sasuke have the ability to control the tides of battle by being able to manually cast barrier. While ninjas like GNW TenTen and Sage Naruto have very strong base damage. There are many builds out there that can help you. If you create a post and share your lineup, I am sure there are plenty of players in the community who would be more than willing to help you build a team.

~Jib