You are correct that I never attempted to move a weight bearing "Loaded Pallet" into or out of a truck, or a trailer, with a 2-Wheel HandTruck/Dolly. However, I have moved tons of freight daily using a 2-Wheel HandTruck/Dolly. But, I do not know what your "Hand Jack" reference is meant to indicate. Or, is that perhaps meant as a reference to a Pallet Jack?
I would not think it a good idea to stack pallets loaded with cardboard boxes containing books. And, to me that indicates pallet movement could be accomplished with a Pallet Jack.
You mention moving "tons of freight daily", but you do Not mention doing this while Completely Loading or Unloading a Freight Truck. A legit Freight Truck is Not unloaded with a 2 wheeled Hand Dolly like we see used to unload a run-of-the-mill U-Haul Moving Van. The Size/Depth of the TSBD Loading dock area tells you the size and load capacity of trucks being received at the TSBD. A Hand Jack has nothing but the user to power it forward or backward. Lifting a load up from the ground requires the user to pump the handle of the hand jack up-n-down. They usually have a max height off the ground of somewhere around 5-6 inches. There is No battery to power the lifting of pallets Up from the ground. The raising is kinda like we see with a floor jack slid underneath a car.