Which would be who? People tend to be immune to their own powers. Those that aren't either die when their powers manifest, nothing training could do to help there, or learn to dela with it, training or not. The X-Men don't really offer much in the way of anything outside combat training, something useless to what most mutants would want. When they coem across mutants with powers they can't just swiych of they just slap a limiting device on them and leave them alone. Rogue could have been helped years ago, it's been long established that her problem is entirely mental and lack of practice but they never make more than a passing effort to actually help.