And yet, he and Spider-Man have buried the hatchet. Hell, they consider each other friends now. Every time they have fought in the last few years now has been more of a "I don't agree with you." kind of thing instead of a "I hate you and want to eat your brains." thing.
If anything, Eddie Brock is a detriment to your argument. As is Flash. Flash started out as a bully. Most incarnations of him depict him as a bully. Then he became Venom. Then he became Anti-Venom and that's who he is now. He has shown MAJOR character growth and hasn't reverted back to status quo. Hell they tried that when they had him lose his memory and it wasn't received very well.
I don't read FF so I can't comment on this as much as I'd likeThe Fantastic Four have snapped back numerous times. Reed died and got better. Thing died and got better. Human Torch died and got better. Thing turned into a pinecone, then reverted back to normal, then got scarred by Wolverine, then got better. Human Torch married Thing's former girlfriend, but she was a Skrull imposter. Doctor Doom's face got healed, then it got scarred again. Anytime Human Torch starts to get too serious the next writer comes along and makes him a cocky goofball again. Fantastic Four is very much the same comic it's been since the '60s, it's just had some modernisations along the way.
At this point, the X-men have gone through WAY too much for them to just snap back. Even Marvel knows this. I mean Magneto is a good example of this. He hasn't reverted back to the sterotypical comic villain he was when he first showed up.X-Men is currently playing with a new direction. It'll snap back eventually. Just like Jubilee as a vampire didn't last.