Will,
I'm a huge Deadhead, but Miles Davis was perhaps the most influential musician of the 20th century. Dropped out of Julliard to jam with Bird and was a first rate bebopper before virtually inventing cool jazz, played a key role in hard bop and modal jazz, invented jazz fusion and was essentially a grad school for John Coltrane, Herbie Hancock, Wayne Shorter, Gerry Mulligan, John Lewis, Gil Evans, Chick Corea, Keith Jarrett, Dave Holland, Tony Williams, Joe Zawinul, John McLaughlin, Jack DeJohnette, Dave Liebman, John Scofield and Mike Stern, amongst many others.
The Dead capitalized on their fortuitous participation in the acid tests and invented the Jam Band genre. So on one hand we're left with a legacy of a huge swath of Jazz and Jazz/Rock of the 20th century, on the other....Phish. Nuff said