>>37491632They probably thought priority moves were too powerful in the 6th Gen, and proceeded to nerf the shit out of them for Gen 7. Not only did we have the Gale Wings nerf, but we also had the Prankster nerf and the introduction of abilities that totally negate priority.
But for some reason, they decided to make terrains much more busted by introducing the Tapus, which just automatically bring in terrains upon entry. The way I see it, they'll find a way to nerf that in Gen 8, only to introduce another meta-changing battle mechanic.