But is that an totally fair comparison when X-Men is a multimedia giant made up of nearly a dozen films, cartoons, anime, live action TV shows, and comics? The Legion had a period of great popularity, but since then they've only been able to muster up one cartoon onto themselves, and less than a handful of meaningful cameos in other cartoons and two live action TV shows. Their comics have even stop being distributed more than once while X-Men has gone basically uninterrupted
There's simply more of a consistent familiarity with the general concept and continuity of X-Men due to its largely uninterrupted mass media footprint. It's not a fair comparison at all.