Yes, every one of those professional announcers no doubt threaded tape.
Not in union shops they didn't. "Those days" are when BM was a thriving format.
Look, you want me to list the stations that paid college kids 2.75 to thread up reels of muzak? There were a bunch. And the day Satellite Music Network was launched, a lot of them got fired. Another way technology led to "job efficiencies."
If you really want to go back in history, there was a time when radio stations had live musicians. But it was much cheaper to play recordings, so all the musicians got fired. Every generation has its thing.
There was a time when DJs sold their own shows. Alan Freed was one of them. I promise you if a DJ did that today, they'd have radio stations lining up to hire them.