top 40 studio bullshit which is all you would’ve known about before
While I agree with you overall, this just isn't true.
We had university radio which would play whatever the DJ was into, because it wasn't programmed.
We had local record stores, which while stocked a lot of top 40, would also bring in albums from small and indie bands that would never get played on radio. They would play it in the store, and have listening stations with headphones so you could listen to an album before you bought it, because you would not have heard it on the radio.
We had clubs that would book bands from everywhere. The club I hung out at had a band every night of the week, and no matter when you went, you would hear someone new.
The music was out there. You just had to get your ass out of the house to find it.
Edit: Also, top 40 stations played what was selling. They were not the problem, it was the stations that were not top 40 that were playing the pablum for the masses, and when it would sell, then it would appear on a top 40 station. By definition, a top 40 station played the 40 biggest selling singles of the previous week. They didn't pick what was sold.
I often heard great bands show up in top 40 because they somehow managed to break through to the masses. I remember when Pink Floyd released an album in the 90s, and the first single on the album got played on the top 40 station because it was selling. This being a time when groups like Ace of Bass, Salt-n-Pepa and Boyz II Men were popular and what a lot of people were listening to. Right there nestled in the hip-hop and dance music was Pink Floyd. Again, because it was selling.
Edit 2: I picked Pink Floyd because it stood out. At that time, in the 90s, it was not a band that young people listened to much of unless they were really into prog rock, classic rock or blazed all the time.