In the late 50's and early 60's, I found that any of my local Cleveland Top 40's (there were generally 3 of them from about 1958 on into the 60's) would play about 1/3 songs I liked, 1/3 songs I neither liked not disliked and 1/3 songs I hated. So I did a lot of switching back and forth, as I never could hear more than a couple of songs I liked in a row.
The big test was the year-end countdown. Even before I started working in radio, I taped the countdown each year and learned to edit with a blade, block and tape to remove the most detested songs... usually about 30 out of 100 songs.
By the mid-70's callout had been invented. The reasons were several. First, 45's were no longer selling much so sales reports were less and less accurate. Second, stations realized that they needed to find consensus songs as there were more competitors trying to take their audience. Callout proved that there were far fewer songs our core listeners liked, so playlists shrunk. One of the reasons recurrents and gold were added to Top 40 station lists was the absence of more than a handful of real current hits.
The late 70's was when Jerry Clifton did a 20 song hit-station in Miami (which famously lost its license!) and was quoted as saying that there were never more than 17 real hits at any given time.