You bring up a good point on internet radio. There are likely tens of thousands if not more internet stations. There is no way to know for sure because there is no central location for all of them. This plays well for over the air radio because the number of choices is finite. It is possible to know all the over the air stations at your geographic location. Over the air radio programs for the masses where internet only stations typically do not. The negative is, say, the student heading off to college in another state. They may listen on their 'device', not the radio, so they are not bound by the geographical limitations of over the air radio.
Internet only stations have astronomical fixed costs that tend to discourage the hobby broadcaster. In addition, the ability to build awareness is costly. The result is there are way more internet only stations that are lucky to maintain single digit listeners at any point. When a college internet only station that has built good awareness among the 10,000+ students can't seem to exceed 870 listening hours a week, that is telling. That's a total of all listeners time number of minutes they listen weekly. The fact is even when locally known, the numbers are pretty miserable with hyper-local programming. I blame this on the listening device. There is so much one can do with the same device, one questions where on that list is listening to internet radio and what interrupts that stream, such as a phone call. In short, the numbers are too small to expect much, if any, listener support and commercially, little chance of being advertising based.
As we move forward, that will likely change. Nevertheless, radio is still in a strong position to maintain over the air listening or at a bare minimum, listening on a 'device'. Over the air radio is still readily accessible, free and reaches the masses.
I doubt over the air radio will become a 'has been' for quite some time. Still, to expect over the air radio to have 'heyday' results is unrealistic. Based on current listening habits, radio easily leads the pack on shear numbers and time spent listening whether that listening is over the air or online.