And then, as all humans do, they'd try to invent shit to try and overcome the supreme weakness of their species, and try to make 'sun clothing' to go out. And then they'd burn to a crisp and die.

If they didn't burn to a crisp and die just from being in existence during the daytime, that is. Troll skin is much thicker than human skin, and even we get pret-ty badly sunburned if we go out. I knew a girl who happened to look up during the daytime and she went blind instantly.