The Philharmonicas, playing "Powerhouse" in 1939. What musical groups would have the stamina and drive to practice as much as these guys must have had to?
It was a time when in order to stand out, it wasn't enough to just posture or fit a template. You had to be good.
I'm sure this is a gross oversimplification, laid bare to counterexamples. But still: just watching this, and trying to picture someone similar doing it today, my imagination fails me.