Good gear comes in several types, and the key to both comfort and protection is the right gear for the right weather.
Good mesh, and good venting, and fairly light cordura/kevlar combinations with CE armor is available. As are lined and warmer for cool weather. And electrics for cold weather. And evaporative vests for really hot.
So the old "it's too hot to wear gear" is mostly just an excuse for laxness or penny wise and pound foolish.
The worst is black T shirts! Or black tank tops.
The Bedouins in the Sahara don't wear black T shirts or tank tops. Full coverage, light, and loose - is cooler.
It was 105 in southern British Columbia on our way to Gillette from Alaska. I had on First Gear mesh pants, my Aerostich Roadcrafter Jacket, and an ORI cool vest. Not cold but not too bad.