You're probably not wrong, but even that estimate at 48 FM's is pretty generous. Keep in mind that Lincoln and Omaha aren't far apart, and the strong Lincoln stations are listenable in Omaha. Lincoln exit signs on I-80 start popping up before you can even tell you've left Omaha. No one (or next to no one) in Omaha, however, listens to Lincoln stations and vice-versa. I suppose both markets might have a few people who live in one while working in the other and don't change radio stations, but efforts to serve both have never worked. KFMQ 101.9 moved to the Springfield tower that housed a few Omaha stations in the early 90's and started trying to serve both. The heritage rock station in Lincoln failed and became "Young Country 101.9," which didn't work either.
Something else to keep-in-mind is that many of those 48 FM's in Omaha are translators and non-commercial religious stations. That doesn't necessarily contradict your point that the market is over-radioed, though, and might even lend more validity to it. I seem to remember Three Eagles thought it was going to move KFRX 102.7 into Omaha and sell it for big bucks. When it finally got the station moved to Springfield and re-licensed to Papillion from Lincoln, it ended up selling to KVSS, which got an upgrade, for a lot less than it thought it would get.
I would also assert that Atlanta might be under-radioed for a market of its size, though it has definitely seen a fair share of move-ins over the last 30 years. Remember, Atlanta radio was designed for the city it was in the 50's, 60's, and 70's, not the city it became in the 80's. People seem to forget that Atlanta had roughly the same population as Tulsa in 1980, and the metro area wasn't much bigger population-wise than that of metro Oklahoma City. Its growth exploded in the 80's, but the broadcast infrastructure lagged behind.