Jaco is barely a Jazz player at all. He does make a contribution to Jazz on one level but is nowhere near hardcore and it would be wrong to call him a pioneer in Jazz. Fusion, yes absolutely. Funk maybe. 'Electric bass' definitely. In Jazz terms, however, he is certainly not a pioneer in any real sense. You would need to look at double bass players for that. The received wisdom says guys like John Kirby (first band leading bassist), Walter Page/Wellman Braud (started 'walking' with Ellington), Slam Stewart (early bowing solos), Jimmy Blanton (first 'soloist' in a mainstream band), Ray Brown, Oscar Pettiford, \\\\\\\red Callender, Charles Mingus, Paul Chambers then guys like Gary Peacock, Scott LaFaro, Charlile Haden (Free Jazz). Jazz bass without Jaco wouldn't look much different whilst pop without Jamerson would be unrecognisable.