You only need to look at player retention in conjunction with how hard Blizzard pushes raid to know its true.
Why would I want to think that? My favorite thing is M+. I’d be more than happy if Blizzard just dropped raids like a rock and focused on my current favorite part of the game.
Simple reality is that raids often help create communities - often to the detriment of the progress of said guild (people refusing to boot a bad player because “they’re a friend of the guild”) but to the benefit of Blizzard keeping folks subbed.