I think it comes down to mass.Roots have the 2 big rotors, that take more torque to spin.The fact that they create more heat is due in part to the surface area of the rotors.

Prochargers are spinning some cogs as do the Roots, but they're only spinning a turbine wheel to charge the air not a couple of 18" rotors.

Procharger all the way, right behind Turbo's