To the extent that any radio operators were offering local "public interest" programming on Sunday mornings, they were not worrying about the Fairness Doctrine.
As someone whose first job in radio was on a Sunday Morning public affairs ghetto program aired on the #1 Top 40 station in the market, I can tell you with first-hand authority that you are wrong. There was significant pressure from station management to make sure that if any opinion was expressed about any political issue, the opposite opinion also had to be expressed. And, if neither opinion was expressed, that was even better.
Not few. Probably over 400 talk shows offered by more different owners then the 2,000 stations offering talk today.
I'm sorry, but 400 individual local talk local shows aren't very many, especially when most of them were lightweight talk about UFO's, health issues, and other non-controversial topics. I remember one of the earliest talk shows on the post-network era radio -- Ed and Wendy King's Party Line. It was an excellent, and very popular talk show. And in the decade plus that it was on the air, there was never a discussion of anything remotely controversial.
You seem to be working under the assumption that talk is talk, and as long as there is no music being played, then it's news/talk format radio. It doesn't work that way. There were not 400 controversial, political based talk shows on the air in the time period you describe.
Well, since that time localism is way down, there are way fewer people working in radio, there are 34% fewer owners, radio stocks are down, radio ratings are down. Sounds like the deregulation strategy was a bust.
On the contrary. That was hardly a bust. Radio lost listeners to alternate technologies. But, thanks to deregulation, they were still able to remain in business. Without deregulation, localism would still be way down. There would still be fewer people working in radio. There would still be fewer owners. And there would be a plethora of dark stations no longer broadcasting at all.