All else being equal bigger diameter wheels with same overall tire diameter means shorter/stronger sidewall. Also, the highest rated tires seem to be 18s in conventional type. Obviously, 19.5s are a completely different animal that won’t air down and are stiff riding all of the time.
I’ve never blown out on a truck, but did on my Class A. It did quite a lot of damage. I didn’t remember the air pressure, so I’m guessing it was lower than it should have been. I can’t say for sure.
On my SRW, I updated to 19.5s just in case. I didn’t feel like I wanted to wait until a blowout to change the tires. I felt good about the safety margin. As I’ve noted, I would have gone with higher rated 18s if I had know about them.