I definitely have to disagree with you, OP. I get what you are saying, but I think you've made things too simplistic. Is it fairly easy to lay down a simple root-note groove? Sure...when you start moving beyond that level, though, well...let me put it this way, there's probably a reason why guys like Nathan East and Leland Sklar are first-call players who are constantly being hired for sessions and/or touring, and being very well-paid for it. And there are bass players out there who incorporate chordal stuff into their playing; some even seem to kind of specialize in it, so...
If I can make an analogy using drummers: Ringo Starr is, as far as I can tell, a perfectly competent drummer, certainly within the context of the music he plays. But there's a reason why Neil Peart has been nicknamed "The Professor" - he's taken drumming/percussion way beyond that of even a lot of other professional drummers, never mind the weekend-warrior types. If most drummers are playing at "Ringo level", does that mean that drumming is "easy"?