Regarding Xavier's uselessness in the films, this is sort of true of the comics themselves. Xavier has often been written out of the team (Starting with a death in the 1960s that was later retconned to be Changeling-AKA Morph), and I've lost count of how many times he's been 'cured' from his leg injuries, or re-injured. I think his biggest leave of abscence was during the 80s, when the team was largely led by Magneto and Storm when he was hanging out with space-wife Lilandra in space, but the status quo returned in the 90s. Even then, there were storylines where he left the team 'for good'. I see him more as a mentor to the team these days, with Cyclops or Wolverine more the mutant leader.