Well I'm by no means well versed in physics, but my mental model of lift would suggest wings + forward velocity generate a lot more than rotors + forward velocity, and that planes move a lot faster than autogyros, so there's more forward velocity to utilize for lift.

Given how much power appears to go into making helicopters rise, its surprising to see an autogyro do it without actually powering the main rotor.

(fwiw, I'm not arguing that I'm correct. obviously I'm wrong).