I think the key here is that it infact had xmen in the marketing. I only checked out one trailer, it evidently had classic X mansion and jet and xmen in costumes and such. There is a good chance this played as a more accessible x men movie in the marketing but with a lead like reynolds. That is, this momentum might owe in some part it's awareness to the shared xmen universe coming off of DOFP. Only upping it for Millers aesthetic is that of Blur Studios and not that 'Singer' look.
Had this movie simply been another Fox stand alone a few years back, things may have played out differently hard to say. I do have to concede that the marketing was super effective, I at first felt it was more just trying hard, 'hey on I'm a rug'. But Hard to deny it worked.
I think if anything Fox will lean on what worked here and apply it to future spin off solos. Like Gambit. Humor aside, they can borrow alot from what worked here. Including having the cameo's be fully realized x men doing fully realized things and not...the blob or some such.
Box office wise fox def made a cbm statement with this one.