I guess a wider frame and wider stance makes all the difference.
That’s a small part of the equation, yes.
Having driven, towed with (many many times stupid chit way more than the truck rated for) and owned or been assigned (company trucks) most all light duty trucks from the last 30-40 years, the differences are numerous to say the least.
Frame, boxed/stiffer vs old c channel.
Brakes
Better Suspension.
Materials technology in general
Stouter axles
Wider longer trucks (in general)
Tire technology and ratings (easy upgrade on old truck of course)
Power and efficiency.
Exhaust brakes
Intuitive grade braking and seamless shifting.
Way higher rated transmissions with 2-3x more gears.
And yes even a fair number of the safety Nannies make towing safer and easier.
And they’re NEW. Or newer.
Where I can cruise down a miles long 6% grade at whatever speed I want without ever touching the brakes or cancelling cruise control, with 12klbs of high profile camper, in 10-15 year old truck technology, on your best day with the best brakes you could ever buy for a squarebody, you’d be right lane doing 30mph wishing for a lockup converter and praying those brakes are as good as the size of the hole in your wallet after upgrading!
And we haven’t even gotten to the comforts that are not present in old squarebodys.
Like this thread started, you don’t know what you don’t know. And from a practical point of view, lack of towing experience and lack of ability to do major work diy is the perfect recipe for very expensive disappointment.