Logan and New Mutants have not been released yet. Deadpool was an origin story about the title character that had nothing to big event. Similar to how Iron Man and Ant-Man had nothing to do with Infinity War.
New Mutants will probably have some connection due to the introduction of aliens.
How he got captured by those anti-mutant people isn't really a character backstory. Since it doesn't tie to his personal history.So we just gonna accept characters having no backstory?
Actually, Suicide Squad and Apocalypse have similar budgets. Not to mention the prequel X-films are spin-offs themselves.Not sure why you're comparing the supposed flagship of a franchise to a lower budget spin-off. Compare X-men fights to Avengers/MoS/BvS