Obviously that older gear wasn’t useless, since real people used it to climb the exact same mountains that people climb today.

It’s pretty clear from the text that they have debunked the idea that modern synthetic materials have outstripped older materials in performance. At the start of their project they expected modern gear of similar capabilities to be lighter. What they found was that modern gear’s advantage is primarily that it is simpler to use. Instead of seven carefully–chosen layers of wool and silk, you can wear a single coat. That single coat is also effective over a much larger temperature range than the older clothes.

Really this should not be all that surprising, as the expertise required to pick those layers has been condensed by engineers into the design of the coat. The modern climber no longer needs that same expertise, just money to buy the coat.

This is the same story of specialization that has powered our economic growth for centuries. You and I no longer need to know how to grow vegetables, or shoe a horse, or design a circuit. There might still be advantages to knowing how to write a sonnet or plan a battle, but for the most part we can leave these tasks to specialists who can get better results than we can. Those specialists in turn can leave other tasks to us. Everyone gets more efficient as a result.