I cant vouch for others mistakes.
... You have to know and understand your setup and equipment. For instance, a trencher is constant and fairly hi flow and pressure, and HP use is up there because of it. Theres where you get heat, as well as constant return pressure not seen on a post driver. Also it is not clear whether your friend used a 1/2 inch, and/or unreinforced hose, and/or a QC. Beyond any or all of those major misses, the comparison to the situation with a pounder is still remote.
... A pounder is very lo flow, only requiring lo rpm to raise the pounder quickly. Duty cycle is approx 50%. Return pressure will reach 25+ PSI for only a split second during the fall cycle. Even in hot weather the fluid doesnt get as hot as a hose in the sun. My reinforced 5/8 hose remains shrunken as if it is in storage, and shows no pulsing.
larry