I just disagree with this statement. He is a guitarist, a bass IS a guitar, it just has less strings and plays at a lower octave. Is a bass player just supposed to keep rhythm? To me that's like saying a drummer should just keep time. If that's the case, why not just sample a bass riff and use that, dispense with the musician altogether.
I suppose if you're just listening to pop music, yeah, the bassist just plays three notes over and over again. But Clarke is jazz, improvisational jazz. And he's been one of the innovators of that instrument in the last 30 years.