You're talking about rock music and the Dead. Drugs were the catalyst, an essential aspect of the musical experience for many of the performancers and the audience. But you're totally right, drugs were the solvent too, dissolving focus, talent, and brilliance to fade away. It's a risk and (sometimes fatal) attraction, I think largely due to the lack of cultural knowledge for responsible and sustainable recreational drug use.
(That was back when the hippies were in charge, before the frat bros took over.)
Q: What did the Deadhead say when he ran out of marijuana?
A: "This music sucks!"
;)
I saw a bunch of Flying Other Brothers concerts, who started at an Electronic Frontier Foundation (EFF) benefit at The Fillmore Auditorium in 1997, and occasionally backed Bob Weir and Mickey Hart!
By the late 80s they had ended up as a really good cover band playing Grateful Dead material. Though there were flashes of brilliance even then, I had a hard time getting up the energy to hear anything but local shows.
I didn't (and don't like) taking the drugs myself, though there was always a contact high / breathing the atmosphere that would tune me up. But the drugs just got in the way of the music.