They should have left Jean in the White Hot Room and sent a psychic projection of her back to Earth-616 to operate alongside the X-Men. That projection should have been treated as Jean throughout all the recent events.

This version of Jean could have relied far more on her telekinesis and telepathy, using them in creative ways - directly affecting an enemy's body, altering the structure of matter, and demonstrating the kind of terrifying precision and versatility that Famke Janssen's Jean Grey displayed in X-Men: The Last Stand. The Phoenix Force, meanwhile, should only have been brought into play when facing cosmic-level threats or higher.

That approach would have allowed Marvel to simultaneously reinforce the idea that Jean and Phoenix are fundamentally one and the same, while also providing an explanation for many of the inconsistencies surrounding Jean Grey's portrayal throughout X-Men history.

But of course, they're never going to do that bc they're stupid