Air cooled cars give some warm air almost instantly, a they do not need to heat up lots of coolant. With a rear engined car of course, some heat is lost in the trunking to bring the air forward, the 500 has a shorter distance to travel than the Beetle. The Beetle carried its heating air in tubes inside its sills. These tend to rot with age, allowing a lot of the air to escape, and of course, more heat loss. A Beetle, or VW van, can give a lot of good hot air when in proper condition.
A problem for later is when the heat exchangers start to rot. Any escaping exhaust gas is then directed into the cabin, not good, so one's nose needs to be on alert at all times.
My first car was a DAF44, an aircooled front mounted flat twin. It would defrost its windscreen as quick as the heated screens today.