Just my opinion, but in order to be an A-lister, a character should be able to consistently carry a solo title. Storm is definitely B-list. Iron Man is A-list. Superman is A-list. Thor is A-list. Storm is not. It's worth mentioning that I would definitely buy a Storm ongoing.
Singing is much, much more difficult. You need to be able to control the tone of the note which is a skill based off of many other more basic skills like tone perception and things of that nature. Basically all a rapper has to do is just be able to maintain 4/4 timing for 3 minutes.
All you ever hear rappers talk about concerning music theory is bars (measures). Scales, modes, octaves, tones, these are things that singers (and musicians in general) talk about. There is so much more involved in singing that it's insulting to a skilled singer to even compare the two.