Well,how soon some forget...With the 6th generation Ford trucks(1973-1979) came the F-150 called the heavy 1/2 ton because the F-100 had been the 1/2 ton for years.They were much more capable in there time.
As for the 3/4 tons back then,in 1976 Ford F-250's were considered great for towing but they had almost the "exact" numbers as the modern F-150's of "Today".
F250 F251 F252 F253 F254 F255 F256 F257 F258 F259: 3/4 ton (6,200–8,100 GVWR max)
F-360: 1 ton (4X4) (8,550 GVWR max)
The new so called 1/2 tons have the same or more GVWR/more horsepower and Torque than the F-250's of yesterday.
Engine Years Power (SAE net)
240 CID Straight-6 1973–77
300 CID I6 1973–79
302 CID Windsor V8 1969–72 130 hp (97 kW)
352 CID FE V8 1973–77
360 CID FE V8 1973–76 145 hp (108 kW)
390 CID FE V8 1973–77 195 hp (145 kW)
460 CID 385 V8 1973–79 200–220 hp (150–162 kW)
351 CID 351M V8 1977–79 163 hp (122 kW)
400 CID 400M V8 1977–79 169 hp (126 kW)
So,I wouldn't say the new so called 1/2 tons are incapable of doing there share of towing travel trailers as the old 3/4 tons used to and still do back when trailers were heavier...
I had the 3/4 ton below when I towed my 35 ft Jayco fifth wheel.It's a 1976 F-250 and it hauls that 8.5 Lance camper just fine pulling ATV's but I can honestly say,my new F-150 pulled my trailers better with more HP and better handling,so I finally sold that F-250 with tears as everything about it was new from ground up and HD.It was a family member for years.
Yes,times have changed and improved all the way up the line but a new so called 1/2 ton is equal to or better than the 3/4 tons of old that got the job done.