But it does need to be ‘awesome’. The cost of casting any of these overcharge spells is freaking ridiculous, imagine how powerful a warrior ability would have to be to justify locking them out of their primary weapon for 20 seconds. That is how powerful overcharges need to be, getting one off should literally leave an enemy in awe and wonder.
EDIT: Or alternatively, they could be made less costly, but that sounds like a lot less fun.