At this point, 19.5s aren't about theory. They've been in use here in the truck camper forum since before I got here. I'd say a conservative guess is 10 years.
I and others have noticed that tire failure is by far the most common one, but also, the most scary failure. No, not frames, not axles, not brakes, not springs .... nope, tires! No, I'm not saying tires on SRWs. Tires generally are what fails on DRWs as well with a significant number of the failures being fronts! It's one of the reasons that I went with a DRW with 19.5s. I wanted a stronger tire.
If you don't believe me, research your theory here. Or, continue to make up a theory on what is by far the biggest improvement people can make to improve their rigs reliability to carry a Truck Camper.
Maybe the posts from some on this thread is about the troll ... if so, great job! ;)