That's an important point. Towing vs load carrying ability. A vehicles ability to propel/tow vs carry/haul a load have different requirements. Pulling 3k vs hauling 3k both require same size brakes and general driveline durability since the gross weight is the same, but hauling that weight will put way more stress vertically on axles, springs and frame. But since rigs can tow WAY more than they can haul, I think you are spot on....
I also think this is the reason you'll see many cruisers with full floating axles and HD housings even though they don't have massive tow ratings, they do carry quite a bit given the size of the axle (R&P) and are likely limited by this axle weight capacity more than the ability to pull (larger R&P)...
That link is very strange.....it says "...offers a 3.3L Ecoboost...", which doesn't exist.
View attachment 532490