It's important to look at their contributions in context. If you only know about what electric bass was like in the '60s then Jamerson's playing is hugely different from what was going on before him. But when you look at the context to the double bass in jazz, and what was going on in jazz in general, it makes a lot more sense.
So a key critical element is that the "innovators" generally have big ears and listen to a LOT of different kinds of music. The "... van halens (sic), SRVs, Victor Wootens, Mozarts..." heard a lot of different things and didn't let genre or style limit their approach. Edward Van Halen is a huge fan of Mozart, grew up loving the classical and jazz clarinet stuff his father played, and learned every solo Eric Clapton recorded with Cream. Then he jumbled all that together with whatever else was going on in his head. Now the most important part is he listened to himself too. See, he apparently STILL can play all those Cream solos exactly like Clapton did- but he's never sounded like a Clapton wannabe. He used that as the template for what HE wanted to sound like.
Same with SRV- 'though I'm not a huge fan and certainly don't think he's any kind of an innovator, he did cop all those Albert King things and put them into a different context with David Bowie. And Victor Wooten developed some of his technique from trying to sound like a banjo well before he hooked up with Bela Fleck.
So where'd Jamerson come up with his technique and his style (two very different but interrelated things)? From understanding the rich history of MUSIC as well as his chosen instrument, and then putting it into what he was playing.
John