Wrong, at around 40mph the torque is FAR lower than at 70mph. It takes a heck of a lot of torque to pull a large vehicle through the wind. And lots of shifts on the highway too if you traverse hills, and strong head wind. And nobody says you have to hammer the gas peddle at each stop light either. You are correct on brakes, but that's an easy maintenance item.
In the end, they are about equal overall.
My father was a highly regarded metal fatigue expert, worked as an engineer for the US Air Force. His expertise was in engine wear and failure. He knows engine wear and fatigue far more than anyone. What matters to an engine wear more than anything is hours, not typical use. Just hours. So, my knowledge is from a real world expert on this subject.
BTW, this is one reason most truck displays have an engine hours counter...