I've wondered where the best fit for the Starjammers would be. Back when Fox was looking for different movies to spin off, I was arguing the Starjammers could be a great X-version of the Guardians of the Galaxy.
Now that they've merged together, I can see the appeal of putting them in Guardians of the Galaxy. Honestly, I would suggest Captain Marvel 2. Have her encounter the Shi'ar maybe right after re-settling the Skrulls. Since my idea for an X-Men film is to make Cyclops the main character, it would also lay the seeds for Corsair as his father in a future series. I just wish Fox didn't do Dark Phoenix twice because the next logical follow up would be to do it traditionally. There's also room for the Brood Saga, though.
Sorry this doesn't really answer the question, though. My guess for Gladiator would be an attempt to get the next wrestler turned actor or something like that. He needs to have a physicality, but he doesn't need to deliver much in the way of dialogue.