I'm just gonna throw this out there. As much as I like Xavier (which is a lot, and he's one of my favorite characters), I don't think he's ever been a good leader of the X-men.
He's a fantastic character, and he's done a lot of really cool stuff, most notably training most of the classic X-men, but he's rarely lead the team in any very effective way.
TBH, I don't think he was around for most of the X-Men's most dire moments. I could be wrong.