I had a long post written, but I can sum it up in two photos of Minnesota races.
1964 Jack 15 Mile. #1 is Buddy Edelen, who set the world record in the marathon the previous year (and won this in 85 minutes). #2 is Ron Daws, who went to the 1968 Olympics in the marathon. Cotton socks. No stopwatches, much less GPS units. No hydration packs or gels. Mostly canvas shoes.
2013 Oakdale Duathlon, men's start. It wasn't even sunny, but they wore sunglasses. Tech shirts and neoprene, though no proof of aid in performance (just fashion). Separate starts for men and women. A couple of $10000 bikes.
I see no improvement, only loss, over 50 years.