I believe that the general quality of popular music suffered a serious decline in the late 1970s. One way you can measure this, since quality in popular music is a rather subjective concept, is by looking at what kind of staying power the hits of the time had. I recently listened to an installment of Casey Kasem's "American Top Forty" from Jaunary 1978, and there was hardly anything in there that people still listen to.
To take two artists that everyone is familiar with, Wings, a band headed by former Beatle Paul McCartney, was on the charts that week with "Girls' School." Further down the countdown, Diana Ross had a hit with "Gettin' Ready for Love." No one has heard either of these songs since 1978.
"Baby Come Back," by the band Player, was at Number One that week, and would be for three weeks, despite the fact that no one at that time or at any time since has been able to tell it apart from Exile's "Kiss You All Over."
I see here that Player's bassist, Ronn Moss [sicc], played Ridge Forrester on the daytime drama The Bold and the Beautiful. I'm sure he appreciated the extra scratch.