Grant:

Rolling start does eliminate the launch advantage of the Turbo S, so that could have an effect...

A couple of things. 3.8 sec to 100 kph is a retarded time. Back when my old 997 S with manual came out in 2005 it was tested at 3.9. 

The rolling start takes care of 90% of the PDK advantage. 

The manual shifts, once moving, are lightning fast. Watch the manual car in the video and watch for the car losing much speed during shifts. You don’t.  

With all those revs you stay in a lower gear much longer which gives you a huge mechanical advantage. 

Weight weight weight.  And no 4 wheel drive which is reduces drive train loss. Made up for by rolling start. 

The standing start is certainly the realm of the Turbo and 4 WD Care with PDK and launch control. Most races have one standing start. 

Bottom line is I trust that GT3 slowly walked away from a perfectly good Turbo. I also know the Turbo driver had to do little to go fast and the GT3 driver working the clutch knows his shit.