ahoi !
i think the original question was very well answered- in turboprops the turbine ( single shaft or multishaft free turbine design) provides a high speed low torque power that has to be translated to a low speed high torque power for the prop since the pure rpm,s of a turbine are not suitable for a working propeller.
in pistons without gearing the engine torque is the same as the propeller torque- in geared systems the same like in turboprops but with a significant lower gearing.
the gearbox is nothing other than a torque converter .
a given power can be achieved by low tq high speed or high tq low speed. - also beyond aviation. a ferrari engine may have the same output like a truck engine but the truck engine will have significant bigger torque than the ferrari. the same power output results in the significant higher reving engine of the car.
in aviation you can see the effect nicely on free turbine props like the pt6a. when you without touching the power levers pull back the props and so reduce the speed of the props the prop torque will rise without changing anything in the output - so fuel flow, gas generator speed and ITT will stay the same. you just exchanged torque for prop speed without changing the power delivered.
@ fella : so the allison basicly was not flat rated above isa when you say you will reach ITT limits before the tq limit even on ground when its above ISA?
cheers !