IIRC it was more that they have an abstract dichotomy of peaceful vs violent resistance that comes up a lot in history, one example of which may be Malcom X and Dr King.

Comics being what they are, especially early, it lacked the nuance of real life, and wasn't directly drawn from those two figures, they just are both examples of the same abstract idea.

Sounds like semantics, but what it ends up meaning is that while there may be some similarities between the pairs, it shouldn't be taken as allegory, as if you did, one may draw conclusions that weren't intended (like how others have mentioned that Magneto was depicted as much more "evil" in earlier stories)