Sounds like false dichotomies. Jaco and Wooten "noodle all over the place" and don't hold down the bottom end, somehow. I guess I'll just have to unhear all those killer grooves they've played in multiple ensemble settings throughout their careers. They have only noodled and trilled high notes, but McCartney, one of the most innovative and influential of bassists, known for composing cello-like lines on bass, we'll just ignore all of that and say Paul was just holding down the root and fifth, or "the bottom end" -
I agree that a bassist must be able to play bassy, while not necessarily exclusively so - but the fret thing always seems to be used as an excuse and apathy towards using the whole fingerboard that I think should not be encouraged.
The opposite is far closer to the truth. There is no $ below the 5th fret, because basic competence with the full fingerboard is more likely to mean you can make some money with your bass and/or music.
I can take the implied meaning as well, but I'm not sure that is universally recognized, and the comments in such threads don't bear out that it is. Maybe the saying should be something more along the lines of "No matter what fret you're on, you're on the first five frets."