They've should have done a smaller, more contained storyline after Apocalypse. Not make a huge cosmic storyline a "grounded" film.
Mutant Massacre - introduce Gambit, the Marauders, and Sinister. You know an actual continuation from the last end credits!
You could have an entire film with the X-Men trapped underground protecting the Morlocks from the attack. Spending more time with Scott, Jean, Storm, and Nightcrawler as they truly become the X-Men and everything it stands for.
Or God Loves, Man Kills (faithful adaptation with Stryker becoming a religious extremist). Imagine the opening scene of that film being this:
They should have given this last film to James Mangold after Logan.