Need is a strong word and the answer is No, they don't need them. But before the movies the
X-Men were the dominant franchise in Marvel and it really wasn't close. The fan base is there and is too big to be ignored.
I would also argue that it was actually the original X-Men movie (2000) and the two sequels (2003 & 2006) that blazed the trail for the dominance of super hero films we see today. Without them I'm not sure we get the same Iron Man in 2008.
The X-Men are as deeply and fundamentally tied into the Marvel Universe as Batman and Superman are to DC (which is why they get about a thousand movies for every one other DC hero movie). Seriously, where is the real Green Lantern project? If Fox can make
Nightcrawler into a positive bad ##$ back in 2003 then there must be someone, somewhere with the creativity to overcome
hot wheels in 2019.