I think metaphors can work if there is a clear link between the metaphor and real life. Orwell's Animal Farm itself is a giant metaphor for Russian revolution. Pigs represented authorities. You can go even further and say Napoleon is Stalin and Snowball is Trotsky. With mutants you can't say they represent any particular minority group so instead they represent all minorities. But then you try emphasizing on a distinct minority problem like voting rights but in doing so you imply this is something all minorities all around the world face which simply isn't true. That's why I think the metaphor shouldn't be the main focus. It should be there as it is baked into the X-men mythos but if X-men delves deep into it it'll break apart quickly. Instead they can give their minority characters prominent roles and be a positive for minorities that way.