Agreed, no place for them nowadays but that in itself doesn't make them sh!t – just heavily compromised in comparison as we seem to agree on…
Unsprung weight – yes, it's important of course but as I said for URTs it's just not as simple as saying that because the rider's weight is applied to the unsprung section of the frame that it's the same as having a single pivot with a swingarm whose weight is similar to that of a rider
The effective unsprung weight on URTs is largely about how much the suspension movement moves the BB vertically upwards since weight is the 'unsprung' mass rather than a fixed suspension structure. If there was no/very little vertical movement (eg a pivot right above the BB and just behind it then the unsprung weight from the rider would be next to nothing… Moments of inertia and all that…
Going back to Mavericks/etc rider weight still does affect the suspension but the design means that the effect is small and insignificant – just like the scenario I described above.