I have enough comics in which Magneto was part of the team... But he remains to be the #1 iconic villain of the X-Men. Also, the fact that he already appeared in 6 films in a starring or supporting role is quite too much especially when the likes of Rogue, Psylocke, Angel, Gambit... You know characters that are seen more as heroes were wasted/sidelined in the movies. Magneto is overdeveloped and has overstayed.
I'd rather take MCU weak villains (as if Apocalypse, Juggernaut, Silver Samurai, Sabretooth, Pierce were that great) if they focus on the actual heroes/the team and not just a handful of characters.