Were there already gatekeepers in the 30s? My understanding was that, radio being a new medium at the time, Hitler was able to do an infowars/Breitbart/prageru style of mass propaganda that was impossible in the existing (print) press.
It's only after the second world war that radio and then television were strictly controlled by the state (albeit more in an attempt to unify and homogenize the nation here in France than to ensure the populace would be vaccinated of anti-intellectualism).