Good morning.
Your comment about the airbags leads me to believe something was not right with your setup. Capacity/lift is a function of pressure and those bags should easily take all the camper weight right off the springs and actually start pulling on the springs.
Regarding 19.5s I’ve only used them (a lot) in commercial applications, construction work. Wouldn’t be my first choice or second choice for rough/off road/ low traction conditions. They are not good all purpose tires as much as LT tires.
I’m sure they can be tailored better to the specific use better than a fleet of construction trucks, but ....
Question, why are you considering upgrading? Based on your signature, I don’t see anything remotely needing 19.5s with a dually.