This a term that only emerged during the period of rock music dominance, and only when there were musical substyles within that would encourage that style of playing. Yeah, you could say that Entwistle was the first true ‘lead’ bass player, beyond any other brief routine soloing which was a trickle down from jazz. Throw in the parallel stylistic breakthroughs from Jamerson and McCartney, which inspired players to struggle out of the roots/fifths straitjacket, and then Bruce, Squire, Wetton, and onward.
All I can say about fusion, which developed at roughly the same time as Prog, is that it was a reaction by younger jazz player to infuse rock ideas into a staid format, so you ended up with more boisterous playing, but with extended harmonic content, injected into the traditional ‘take a solo’ format. What I found interesting was the development, in the late 70’s, of a different ‘lead bass’ approach…that of Peter Hood, Barry Adamson, Steve Severin, and so on.
What I never understood was the point of “piccolo bass”. That’s an oxymoron, just a four string guitar.