They are though. By all accounts, they function exactly as prequels do. The unusual continuity situation blurs the lines, but outside of confusing the general audience it makes little difference.
If the X-Men series nailed details like costumes at some point in the past 17 years then maybe people would move on. The tease at the end of Apocalypse is decent progress but arguably not enough by now.
I am a huge fan of Singer's X-Men universe (when it is good, anyway) but I can fully understand the frustrations of fans who don't feel the series is reaching its potential. There's a ton of wasted characters and stories left behind, and while I'd argue that Singer can make a film good enough that it doesn't matter, we could be at a point where the films are as good AND more accurate.
O/T - Homecoming looks potentially great to me. Parker looks like an actual kid, at an actual school. Feels like it is going to nail the John Hughes tone they are going for. I saw some emotional stakes in the trailer too, and Keaton looks quite intimiating. It probably won't dethrone my beloved Raimi series, but I'm optimistic.