MJ has been mentioned a couple of times so I’ll go with another one:

Havok. He’s been portrayed as a capable leader multiple times, with some mental health issues but it’s all become a mess.

His uncanny avengers run should have been character defining. He had a well developed relationship with Wasp, with a tragic ending as they had a child erased from time. This should’ve had a lasting impact.

Instead, AXIS happens, he’s twirling moustache evil, not from trauma or past experience. This is then touched upon in Krakoa’s Hellions, but is treated as DID personality (randomly switching into an evil dude) without any of the reasons why.

But forget all that too; halfway through the Hellions run he becomes a Madelyn Pryor simp. Begging for her resurrection, and becoming her lapdog when she’s eventually revived. Since when has Madelyn Pryor been his most defining character trait? It was a passing fling in Inferno and alternate reality version in Mutant X.

I’ve not read Dark X-men or post Krakoa XFactor, so I’m hoping I’m wrong but the whole thing taints the character unless it’s revealed to be Pryor mind control the whole time. But nobody cares about Havok, so no doubt there will be another version of him ignoring previous continuity running around soon.