I believe the main difference between Malcolm X and Dr. King had to do with different approaches. Dr. King’s approach was slower because it involved more people, more negotiating and was completely non-violent. But at the end of the say it was the only one that worked or could work. Otherwise the members of the movement would’ve been portrayed as thugs, criminals and terrorists by the media.
No serious politician with serious power would’ve worked with people seen as thugs and criminals. Malcolm X’s approach was more combative. That Africans have been in America for three-hundred years and should’ve gotten that freedom three-hundred years ago and “we are mad as hell and want our freedom now”. Which is certainly understandable, but it would’ve never worked had the members of the movement used violence even just to defend themselves.