Driving on the beach or in deep sand is the only area where I believe there is a legitimate complaint with 19.5's. Yes, you can't air down 19.5's. Pizza cutters? The 245/70-19.5's are about the same width as my stock 265/70-17's. Offroading in terrain that requires "offroad" tires? How many truck campers that are this heavy are really going to the extreme 4x4 conditions that a slightly softer tread compound is going to save their bacon?? Any forest service road or gravel road will certainly be fine with the 19.5.
Finally, I want the safety margin. I could be careful with my camper load and be at 99% capacity of the load E rated tire without a lot of effort. This is also a lot cheaper than getting rid of my low mileage 5.9 Cummins and get a a new dually.