Well, I was in a community of musicians in the 70's, and they would certainly agree with your assessment. And it's true to some extent: there were very few innovators after the 70's in rock and pop music. But, especially since I was disengaging from my 70's friends in the 80's, I found there to be whole other worlds of music, and experienced the condemnation of the 70's community as snobbery.
What was especially repugnant, it seemed, to the 70's group was music with a beat, with rhythmic emphasis - with African-American/African influence. True, some of that was embodied in "disco", but there was more than "disco" going on. I recall a comment you made once that that rhythmic "soul music" was the perfect inroad to world music.
At any rate, if my speculation is accurate, then indeed Prince wouldn't have held any interest to the 70's-elitists.