On 'people who do Jaco better than Jaco', I'm reminded of Stevie Ray Vaughan and Jimi Hendrix.
Much as I loved SRV's music, one was the innovator, the other was the imitator.
It's the creation of a new paradigm in music which is the real achievement. Einstein conceptualised relativity, but others too it further - does that diminish Einstein's achievement?
As for Jaco's mental illness and drug abuse issues; they are desperately sad but no doubt as intrinsic to his character and creativity as Van Gogh's, for example, and cannot be bignored to understand him in the round.