Well...your warrior can use staff.
Yes well, and then I can't use Knockdowns because it targets different armor type... So there goes my RAM, Stomp and Cripple..
Same is when I build Summoner (not stat investment needed) and want to run around with Sword or any other physical weapon- unless I will ONLY summon Blood infused Incarnate all the time- I will again just put myself on disadvantage all the time
Because in theory the whole build system is super open, but in reality- its restricted by armor system.