Even as modest as the CUT numbers sound, they are a far cry better than the older tractors, many of which pulled around over 4,000 pounds in just machine weight with much less than 20 horsepower. I recall when I was a kid, our school had an International LowBoy tractor for mowing. It was not that large but very heavy and had around 18 horsepower. I suspect with mower it weighed nearly 2500 (or more) pounds and was advertised as being a very powerful mowing "CUT" type tractor. Now, one can go to Lowe's and buy a tractor he/she can about hand lift into the truck that has more than 18 horsepower. As a poster mentioned, it is all about torque and gearing. One can get a lot done with a lower powered engine that is diesel if it has low enough gearing, big enough tires and enough chassis weight to harness the power. I have had the priviledge of owning both a 4310 and 3720 JD. They are the same size and weight and have the same chassis. The 4310 was 32.5 flywheel and 25 PTO HP; the 3720 was 44 and 35.5. They would do exactly the same thing. The ONLY difference was the speed with which they would do PTO work, nothing more. The 3720 would not pull a bigger box blade, nor load dirt or mulch any faster as it was traction-limited. In my opinion, the 4310 would actually PULL more, despite its lower HP as it did not overwhelm the tires as much. In this case, as in many others, raw horspower is not that easily accessed or used.
John M