yeah but the helmets would be bumping into those humongous backpacks.

I don't like a backpack during a strenuous ride because I do not want to be restricted in breathing or movement, and the back gets very sweaty despite the mesh thingies that bike rucksacks have. Moderate rides, commuting, fine. I see there's hotter weather than what I live through.

You have to reduce the amount of stuff you haul along if you want to ditch it.