Expectations have changed. Today we drive our cars with the windows closed at all times. In every sedan Mercedes up until the W123 the ventilation window was a feature that allowed for augmenting existing in-cabin ventilation. The W108/109 has wonderful ventilation if the car is moving. The moving car has clever air exhaust features that allows for the car to exchange cabin air well enough to keep the occupants comfortable until air conditioning is needed. Standing still the blower is indeed weak and noisy, but it will keep the windshield from fogging assuming its clean and the flow is dedicated up via the control. Also, assuming you have the correct thermostat for extreme cold weather driving and the heat control levers are working properly the system will warm the cabin very well. In middle Tennessee we typically do not seasonally change thermostats so I just bundle up when driving the car in temperatures below 10 degrees F.

For the driver (the most important occupant according to Mercedes) the dash vent on the far left(right for right side drivers) has a lever to allow for direct outside airflow. which while for the benefit of keeping the driver cool and alert it also serves as added anti-fogging for the side window.
The W100 600 first released in 1963 and the W111/112 released about the same time were the first Mercedes to feature the same ventilation tech found in the W108/109.