I don't know if you can say the same about Ditko's effect on Spider-Man in the long run. Stan worked with JR sr when ASM started to push Marvel into being a serious challenger to DC's numbers. It did overtake Fantastic Four as Marvel's top seller.
I agree with you about Magneto but I think part of that is because Claremont took Doom's origin as his template to give Magneto a proper origin. Even Byrne called him out on that. and called Claremont's Magneto revision as a "half-assed clone" of Doctor Doom. Admittedly it's a stretch to say Stan's mixed the two up but Stan did have a notoriously bad memory. So did Kirby at times. They were both getting up there in age when they gained their greatest fame.