Cult, yes.
Fascist, no.
Isolationist and mutant supremacist with some creepy authoritarian overtones, yes. What's missing to make it fascism is a commitment to conquest and domination. So far, Xavier isn't seeking to subjugate and rule the rest of the world.
The way I see it is this: Marvel spent several years turning the Inhumans into the X-Men. Now, they've turned the X-Men into the Inhumans. Krakoa is similar to what Attilan used to be. There are parallels between Xavier's role and Black Bolt's historical role. Apocalypse, Sinister, etc. similarly parallel Maximus's historical role, and so on.