I don't think anyone argues that the most capable heavyweight off road bike is the KTM 950/990. Service intervals, road manners, and reliability is why many if not most shy away from them and turn towards the GS/GSA. Off road ability is by superior on the KTM and the reasons are suspension and the 21" front wheel.
I did not start my riding lifestyle as early as you, but I did start in 1970 when 19" fronts were the norm. I had a 380 Greeves but mine did not have a leading link fork, it had Cerrianis and 21" front and far out handled the 19" bikes.
Sand and soft dirt is what the OP was asking about on a heavy bike. Sand is similar to water and a flat bottom boat planes above the water, floating, but it still needs a rudder to steer.
Floatation on sand does not make for good steering, there is NO control and if you are trying to use steering input while the tire is floating on sand and it happens to dig in it dives right or left and plows. Look at how many pics there are of GS/GSAs laying on their sides in other threads.
Your arguement is also flawed on the point of heavy bikes being somehow different that the 300# ish 650R that JC rides. My arguement for that would be if a 19" worked better anywhere except the street than Cyril Despress, Marco Coma, and Gaston Raiher would have ALL used on when racing in the sands of Africa on their 500# ish bikes....yet NONE did.
Just because someone is not as old as you or has a different opinion does not mean they know nothing.
OP put a 19" on your sporty ans enjoy the street riding and the occasional hard pack fire road. Follow old farts ideas and ride it in the sand and post pics of it regularly laying on its side....I love those.
it is easier to ask for forgiveness than permission