Well the sequels are relevant in the sense that they're indicative of what the suits were thinking when they greenlit them and that was: "more guns, more action, more horror, more vampire stuff!" not "more content faithfully adapted from the comic books!" If the first movie really had made it easier to pitch comic book concepts then surely the latter would have been the case and not the former, no? And that's the suits that actually made the thing, never mind ones at other studios.
That plus the fact that the first X-Men movie sort of slipped in the side door pretending to be a science fiction movie and was still mostly ashamed to admit it was really a superhero movie.