pniichols, I can see nothing wrong with your logic. When I originally got involved on this posting, I thought I was on the 5th wheel site( senility has it’s downfalls)....we have both a class c and a 5 th wheel. When I mentioned the 19.5’s, I was referring to the truck, thinking I was on 5th wheel site! . We haul very heavy loads with a SWD truck, another topic for another day. The 19.5’s allowed us to have “much” greater rear load rating.
When we put “new shoes” on our class c, we will do the same as you. A much taller, 16” tire, and recalibrate the speedometer. We’re running 4.30 gearing, taller tires will be a huge plus in many ways!