Most superheroes have a legacy character:
Iron Man - War Machine, Rescue, Iron Heart
Thor - Thunderstrike, Beta-Ray Bill, Jane Foster Thor
Captain America - U.S. Agent, Patriot
Spider-Man - Miles, Silk, Spider-Gwen
Hulk: Skaar, She-Hulk, Red Hulk Amadeus Cho
Ant-Man(Hank Pym) - Scott Lang, Eric O' Grady
Hawkeye - Kate Bishop
But there are very few mutants that have legacy characters(I may have forgotten some so please list):
Wolverine - Laura, Daken
Magneto - Polaris
Phoenix(Jean Grey) - Rachel
Should other mutants have legacy characters or should they remain unique?