HD trucks of 20-30 years ago had similar tow ratings to today's V6 trucks. Heck, the 2006 Ford and GM base V8 engine trucks had tow ratings in the 7500 pound range. So yes, I agree that today's engines are making a lot of horsepower and torque compared to many years ago. Specific power output has increased a lot even for naturally aspirated.
Ford's old inline 300 had about 140 hp and 250 lb-ft of torque, but available at 2000rpm which is where many people drove. And those trucks weighed 2000 pounds less than today's trucks.