Honda AT and Supertenere (original one) were answer to early PD races that were won by BMW twins with scaring consistency. In fact Honda that raced in PD had almost nothing in common with AT750 and very little in common with AT650, the first one. AT750 does not carry one single part copying PD bike. Even frame different. It is pure marketing.
Yamaha Supertenere 750 have VERY little in common with PD Supertenere. Very little. I once (together with friend who are S10 fan) made lists of what is shared between PD S10 and "civilian" S10. That was funny....very little indeed.
DR Big was developed in 1987 as answer to multi PD racers with attempt to match raw power it had to compete against.
Surprisingly, probably because of tight budget and bikes built not by something like HRC but by Gaston Rahier own shop they share lots with civilian version 750 (and consequentially 800). So - DR Big stock closest to DR Zeta PD bike mechanically. Just for info - KTM was almost non-existent in PD at time it all started.
You are totally spot on about all this deal. Those are all open piste bikes, not meant to be taken into any at all technical stuff. People still do it, but it is like trying to hit small nail with sledgehammer. Pointless really. But I see many folks getting fun from lifting heavy bikes and crawling through tight terrain that any light enduro would simply fly through.
I use gym for heavy lifting
and my tiger only for open piste.