I'm sorry, but that position is not accurate.
Before viable FM came on the scene in the later 60's, we had situations in major markets that can be exemplified by Cleveland in the later 50's and early to mid 60's: 8 AM's, 3 MORs, 3 Top 40 and two R&B stations. 3 formats.
FM came and we got format division, like album rock and chicken rock (later called AC) splitting out of Top 40. Later on, we got rhythmic Top 40, too. And so on in every format.
The we got to the late 80's and Docket 80-90 that allowed more FMs, and many move-ins. Many stations lost money as there was no new revenue.
So what was happening: Owners picked the most profitable formats, and we went back to having multiple stations in the bigger formats.
Consolidation, beginning about 6 years later, allowed operators to have up to 5 FMs, and so they tried to make each one complement the others. Often that meant accepting a top performer or two, a couple of middle performers and a lower performer. But they could package and sell them as a group or in combos. So we got more variety after consolidation than ever before.
Obviously, though, there are and always will be songs that cross the borders of different stations and formats. What makes each station different is the rest of the library that no other stations duplicate.