Are Monks underpowered, balanced, or broken?

[ken-do-nim]

In my experience, the most important monk ability is the stun. It gives them a role in combat; tumble and move over to the foe causing the most problems and try to stun them. Problem is, many of the foes they need to stun (gee, like that dragon) have excellent fortitude saves.

One option is to remove the 1 stun/round limitation and 1 stun/level/day limitation. Instead, any hit that hits by 5 more than needed is a stun chance, and every point that it hit beyond that lowers the save by an additional point. This makes a flurry of blows more deadly because each hit has a chance to be a potential stun.