What labels pushed on the radio did certainly feed into what people bought, though.
Yes - but the Chart Shows (both the BBC and the commercial stations) were the places where the stations were obliged to play songs, during the daytime, that weren't on their playlists.
We have the same thing here with JJJ hottest one hundred. It is still mostly local underdogs so that is rad, but like you noted, the tides are changing thanks to streaming and every year gets a bit more mainstream.
However, since streaming, that equation has totally changed.