"In that vein, when I think of the best rock bassist, I think he should be one who leads a rhythm section while providing other members the freedom for musical development and experimentation."
Heh you just described what could be several outstanding bass players over the years... Geddy Lee among them.
And with all due respect Paul McCartney has no place on any list of best anything (favourite I can see, but greatest?) He is a solid musician, but mentioning him in the company of many bassists listed in the post, is like saying Charlie Watts is a "great" drummer.
Anyhow, these "who is the best <insert instrument here>" are silly when you think about it. There have been many GREAT bass players over the years, some better than others overall, some more proficient at slapping or on fretless instruments.
And unless I missed it, no one mentioned Chris Squire, Gary Peacock or Jeff Berlin (incredible bassist).
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Hendak, Jammr - DAOC