The byakugan users are dumb when you think about it.Imagine the byakugan on a guy like A or naruto, they would easily be considered overpowered (more than they are now), but the hyuuga clan is apparently to proud to develop real ninjutsu.
Neji could have reached kage level if he focused on learning an element or two.
EDIT:
Only lee can't use ninjutsu.