I was thinking about this. Maybe The Beatles greatest contribution to popular muic was to make the self contained (writing own songs, some control over the process of their music) act the norm. Singing factory produced music chosen by a manager has not been cool since.
Dylan's was to make singing about nothing but love etc also very uncool. Ever since, acts have had to have a certain "depth" to have any cred.
And Elvis? He established the white, sexual rebel male as the template for popular music. The music itself wasn't enough. Bye bye fat old Bill Haley or black Chuck Berry as the future of rock.
I struggle to put one of these achievements over the others. Each one is essential for rock as we know it today. Though of course progress isn't always good. I guess you could make a case that popular music was just as good (maybe better) when it was being made by less image conscious acts singing professionally written love songs, rather than pretentious hippy psycho babble written by a bunch of stoned rich rock stars pretending to be something they're not.
I guess I'm thinking Elvis and The Beatles contributions to music were different but no less significant.
And I should have used the word "popularised" for all 3 above. Beatles weren't the first act to write songs, Dylan not the first to sing about something other than love and Elvis wasn't the first white boy on the scene. But I think these are the three acts that made these trends popular.