If a song is a "dud", you can play it until the listeners ears bleed and it won't sell any better - and your ratings will suffer as well. Bad is bad, no matter how many times you play it. Along the same lines, you can run ads repeatedly for a pizza place, but if the pizza sucks the ads aren't going to fix that.
Sorry, but that is dead bang wrong. While you cannot turn a total stiff into a hit, if a song gets any airplay, even if it is a total piece of crap, it will sell better than it would sell without airplay. That doesn't mean it will be a hit. But a song destined to sell maybe 1,000 copies at best when the band who recorded it pushes it at gigs would increase sales to maybe 10 or 20 times that with radio airplay. That would not make it a hit. It wouldn't even crack the Top 200.
But it would sell better with airplay than it would without.
Along those same lines, if you run ads repeatedly for a pizza place, but the pizza sucks, that pizza place will get large numbers of new, first-time customers who order a pizza. When they discover that it sucks, then they won't come back a second time, but until words gets around that their pizza sucks, lots of ads will bring in new, unsuspecting customers.
There's a story about that principle. A guy is walking along a street and he hears people behind a wooden wall chanting "12, 12, 12, 12, 12". The guy sees a little peep hole, so he looks through, and gets poked in the eye with a stick. As he walks on, the new chant is "13, 13, 13, 13, 13". Good aavertising will get people to look through the peep hole, no matter what's on the other side.
Besides, the real issue is that people working in radio need to convince people in a position to decide where ad money should be spent need to promote the idea that radio advertising works, even if that's a lie. Radio stations don't make money by convincing clients that the client's product sucks. They make money by convincing them that radio will work for them better than any other medium.