It’s bad enough that Simon Kinberg entirely fails capitalize on this unity in any meaningful way, but he even makes things worse by having the end of the story shut down any possible further development for the ensemble by taking two incredibly important characters off the proverbial chess board: Professor X and Jean Grey.
Obviously a lot of this extends from general disappointment in Dark Phoenix, but what makes the movie particularly unacceptable is the fact that it had a lot of opportunities that it simply squanders in important ways.
This begins with the fact that it is supposed to be a film featuring a version of the classic X-Men team that has been operating for 10 years together – but nothing actually substantial comes from that cherry setup because of many unfortunate plot choices.