Heat alone is also pretty shitty at defogging windows, it works a lot faster when you have the heater and AC running simultaneously. Which you cant do in a Beetle, since most of them didn’t have AC.

In modern cars the air first goes past the AC, where it cools down and loses most of its humidity due to condensation. The it passes the heater where it heats up again, further reducing the relative humidity. That way you are blasting hot and dry air on your windshield, which defogs it much faster than blasting it with hot but still moist air