Not going to lie, I'm really digging the vibe of a battle maniac co-protagonist that slowly gets stronger than everyone else EXCEPT the other MC by being an unreasonably durable knucklehead.
I hate to sound like a cliche by referencing something older, but it's like Naruto, if Naruto was mentored by Itachi and Itachi was the main protagonist. I actually really like this. It's refreshing and pretty novel, at least in my experience.