It seems confirmed in the latest chapters that Kanki is weaker than Zenou, his axe. I'm not convinced Ousen is particularly that impressive either, but we haven't seen much from him to be fair. In other words, they are capable fighters in their own right, but by no means are they monsters.
We already have 3 martial monsters within the Qin6 group, it's fine that 2 of then happened to be more strategy focused.