I'll go on record saying there's no possible way this is worse than Apocalypse, mostly because Apocalypse is bad in ways that could only be surpassed if you set out to intentionally make a worse movie. Writing so bad that even Fassbender can't carry a scene, rehashing an iconic scene from DoFP that only demonstrates that you don't understand what made it so good in the first place, a terrible look for the main antagonist, terrible supporting villains, just awful.
The main problem facing Dark Phoenix is that it either revolves heavily around Sophie Turner, who is still largely unproven as an actress (I don't think she's had the opportunity to prove she sucks like Emilia Clarke has, at the very least she's spent years portraying Sansa very accurately), but you know they will crowd out her screen time with the bigger names in which case why the fuck is it even called Dark Phoenix. And apparently on top of the fact that they have McAvoy, Fassbender, and Lawrence all fighting with the titular character for screen time, they also have Jessica Chastain playing a Shi'ar character.
The two things I'm confident about are that if Dark Phoenix is awful it still won't be worse than Apocalypse and it won't be Sophie Turner's fault.