I have no idea what you're trying to say. Yes it's not "just physics" that causes the FCC to regulate the content of broadcasts on radio and TV airwaves. I thought that was obvious.
Even if the FCC chose not to regulate broadcast programming, they or some other body, would still need to enforce rights to frequencies. That's their raison d'etre. Content policing is an added function, which the law has found valid in the past precisely because frequencies are limited. I can't see such public interest legal opinions being newly formed today.
The FCC doesn't regulate content on cable TV. Technologically, there's no reason cable radio couldn't have existed.