What the SAE standard does is allow the manufacturers to pump up the TWR using the minimum 15% pin weight recommended for fifth wheels. To do that they use as much pin weight as they can and still keep it SAE compliant. So if Ford allowed you put 2,000lbs of pin weight on the truck that would put the TWR out to 13,335 lbs to be SAE compliant. So my next thought was that is was ok to have a lighter overall trailer weight and the pin weight could be higher as long as it doesn’t exceed the payload and rawr. Ford said no to that and said that exceeding a pin weight higher than the %15 of the TWR in the towing guide was exceeding the limit. I’ll take that as the maximum pin weight allowed for the truck.
I agree that we are all used to having pin weight only limited to available payload or RAWR. Ford is is changing the rule by limiting the TWR well below available payload and RAWR on the F150 most likely because of the SAE standard. Vehicle dynamics are quite different between a truck alone loaded to GVWR/RAWR and one that’s pulling a 5th wheel that’s 11,000 lbs with 2,000 lbs pin weight.