Good points. Yep just like old bubblegum.
There are still a few good orig melodies (which is what that gen was good at) I still hear so there is talent. And not a shot as I hear some good stuff now days. But the preponderence of stuff back then.
There was so much good music coming out that at the time you couldn't listen to it all and it took years to catch up.
But original melodies, whether rock or even bubblegum, that is what the Dylans, CSNY, Beatles, Elton John, (the Bernie Taupins, Jimmy Webbs) ect ect could do so well.
Maybe it was the time. In say 1957 when some of these guys were learning music, it was a quiet time, you had maybe one tv station, perhaps their teachers connected with them and as you say the time was right and fertile.
Then drug use just let it all happen as these dorky kids of the late 50's creatively blossomed around 1970.
..dorky... Buddy Holly just popped into my head.. one of the original greats as well.