Quick recap: Elvis ruled the airwaves until 1964 when the Beatles arrived and took over. The 70s were less dominated by a few acts but believe it or not Abba and the Carpenters had a huge # of top hits along with Paul McCartney and as the disco craze hit the Bee Gees. Not how I remember it! My favs like the Allman Brothers, Eagles. Steely Dan, Clapton etc were not bringing in the most airplay.
In the 1980s, MTV started shifting music to a more highly produced and visual medium (eckkk) with Micheal Jackson and later Madonna trailblazing and generating huge listenership. Queen also was crushing. This decade also had more folks crack the top song category.