Re: wat if they built up to x men, like avengers?
I think it could have worked. not as huge as Marvel, of course, mainly because it would have been on years 2000-2001-2002 or so, and the boxoffice around that time wasnt as big.
But I think the better approach would be to do solo movies to the actual X-Men, and not Xavier and Magneto. This way, all the lead X-Men would have had a great development before the first team movie, and they would have been a bit more popular to general audience before the team movie too, so this way the team movies would have put most of the focus on only Wolverine, but would have been even more ensemble.
But anyway, as many fans have said, X-Men work better as a team, and at the end of the day, all started as a team, since the 60's comics where basically Xavier having a team already, with the backstory of each x-man beeing adressed from time to time, instead of a solo comic first.