Back in the 80s when I was a kid in Brazil, my father, a truck driver, drove a Saab-Scania Truck, with a 10 SP ZF fully synchronized transmission. That's how I learned how to drive back then.
I remember going thru the mountains with loads up to 80.000lbs, sometimes 85.000 lbs
on the trailer, not including the truck's weight.
We never had clutch or transmission issues. I remember my Father's LK 140 Scania V8 engine 14 Liter engine, had the clutch replaced at 700K miles.
So that tells you synchros do last long as well, also using the clutch to shift every gear up and down, no issues.