“Jerry Garcia was at times resistant to extended chord changes”

Do you have source for that? His opinion had certainly changed by the early 70s when he was writing songs like “Eyes of the World” and “Stella Blue”.

I used to play “In a Silent Way” for my Dead Head friends and tell them “This is what the Grateful Dead are TRYING to do”. Some were into it, some scoffed. But in his autobiography Phil Lesh talks about seeing Miles’s electric band and pretty much quotes me verbatim.