When developing the engines for Ford, International was told not to make it more powerful than the 460 gasser, which in the bad old days of low compression-smog-CAFE standards only put out a couple hundred. Even in 1994, with the turbos as a stock option, the down pipe was so restricted that the diesel still only made 210 hp (to the 460's 215 or 220) The diesel option was just a nod to the growing popularity of diesel powered private vehicles in the early 1980s, not a true effort by Ford to put out work trucks with long lasting durable engines.
The V8 layout is also not an ideal form for diesel, it was called for to fit in the same space as the 460, and as some here have found, the Ford engine bay was not well suited to straight 6 diesel engines, which can make piles of HP and torque. Again, not desired by the wonks at Ford trying to keep the 460 as their premium engine.
The thing you need to remember is that even though they are not powerful, they will run a very long time past the time when the gassers are wheezing and need a rebuild.
One more item: HP ratings and $7 gets you a coffee at Starbucks. Torque is what gets work done and the diesels have gobs.
My N/A is rated at 170 hp and pulling a 4000 pound trailer up a 8% grade will only go 40 mph, but will do it all day long. Thanks goodness for the giant radiators.