I have done lot of tours on GS. Total milage on my odo is 27000. My bike has been to Ratti gali 2 times and 1 time on Noori Top. Still its clutch plate is going fine, feels no power loose.
My be GS Rider in this trip was engaging too much clutch, or clutch was not properly adjusted which resulted in fried clutch plate. In my opinion climbing performance of GS 150 is better then Ybr G.
Cant say anything about YBR Z