I could easily hang a 5lb weight from my fretting hand, but I see little need.
Sissy comments aside,(yeah, some have earned this) some of us have spent many years developing our technique. Mine does not involve supporting or moving the bass with either hand, nor should it. As a mostly fretless player, the left hand grip required to balance the thing would lead to piss poor vibrato. As also a mostly 6 string player, the necks would be virtually unplayable due to the width.
It is possible (granted maybe not entirely convenient) to have them so they require NO support from either hand/arm - ZERO - I don't know why this has to be repeated so many times... As to neck width it is the same as a jazz bass. I switch between it and a 5 string fretless F-bass and an upright with no issues (the upright has far more ergonomic demands).
Not trying to convert you. If it's not your thing, cool.