It looks like level does make some sort of difference. You did end up getting 10 assists after all. With that being said I agree and think the leveling should work more like it does in pve. If you're character is a low level than you shouldn't even be able to play iron banner. The only time I could see that being a problem is if iron banner ever got its own game types but as it is now it's not like low level players would be missing out on anything since it's pretty much just control.