How could the X-Men possibly fight Wanda?
The first time they encounter Wanda in the mall, she kicks everyone's butt.
In the end, Professor Xavier says he failed them, because he should have taught them how to fight someone like Wanda.
But could they possibly do so? Her powers are disproportionaly greater. She has her own powers and also can control everyone's powers at will with no difficulty.
Even if they are smart and very coordinated, she can easily overpower them all. She can only be beaten by telepathy, by Rogue sneaking close to her and touching her, or maybe by this Dorian boy who can turn off anyone's power.
(Evolution is all I know of X-Men, except a couple movies)