People are people. Given a choice, the majority of the target audience for classic hits will respond well to the tighter, more focused station, regardless of the size of the market.
And there is a logical reason for that. Yes, there are people who think radio has an obligation to provide wider playlists, but we know they constitute far less than a majority and have little impact on the ratings either way. Radio, being a mass medium, programs for the majority, who have grown up
expecting radio to be a aural "comfort food". They want familiar (even to the point of still loving songs that the "wide playlist" advocates think are burnt to a crisp) and they want it consistently every time they tune a station in.
The Joplin example is proof of that. Sure, the formerly predominant station had a wider variety of music, and our little group of advocates for same will applaud them for it until their hands bleed. But the listeners are choosing the other station, with the tighter, more researched playlist ... because every time they turn it on there is something familiar playing, which comforts them. So the ratings went up and stayed up, and I bet if we had billing numbers for that whole period of time we'd see that the wide playlist station has been losing ground there as well.
And lest you think this is some new phenomenon: At one point in my career, I was part of the programming team at a top-40 FM with a country sister AM. The latter's numbers were sagging and the decision was made to update the format to a "pop country" approach. You never heard more Juice Newton and John Denver in your life. The station was rebranded "Country 16" (we were at 1590), there were jingles all over the place, the song-spot-song-spot clock was abandoned in favor of three-song sweeps and two-minute stopsets, and the airstaff gradually was replaced with refugees from the 50,000-watt flamethrower top-40 AM in the market. (I even wound up with a three-hour daily airshift at one point.) And the ratings went up.
Yet we had a thorn in our side, which was one persistent older man who called the request line at all hours, day and night, multiple times a day, insisting that we were a "country and western station" and complaining that we weren't playing any western swing music. (The irony was that the station had never played any in the ten-plus years since it had flipped to country from top-40.) Eventually, it got so distracting that we had the phone company trace his calls and they then advised him that he would be disconnected if he continued making harassing calls to the radio station.
Now you know why I get tired of the "wide playlist" argument so easily.