Totally disagree with the layers philosophy. Way too much fuss. In mid-winter London I wear a t-shirt and a jacket. Perfectly warm. Just get a good jacket. Easy on, off, no ceremony.
Layers are also a must if you do outdoor winter activities. You want to remove layers when you're active so you don't get all sweaty, and put them back on when you rest. Because sweat + cold wind is a really nasty combo.
Having said that, as far as I can tell most people in the city here don't do much winter sports and just own like 3 different coats for different weather.
when I'm going out for a while in the winter, I like to wear a cotton shirt, a wool sweater, insulated vest, a medium-weight windproof jacket, and a mostly empty backpack. if I get too warm, the vest and possibly the sweater can just go in the backpack. with this setup, I can be comfortable at any temperature from 30F to 60F without having to hold onto anything I'm not wearing. on really cold days, I swap in my heavy winter coat.
I know because that's what I use regularly for long walks and even bike trips
In London I had one jacket, mostly to protect against rain, but it was also an extra layer.
In Copenhagen, which has similar winter temperatures to Berlin, I had to buy a thicker jacket for the winter. I've worn the new jacket on trips to London and felt hot.
-20°F (-30°C) is a real change in perspective of what cold is. You absolutely need layering, as the equipment you need to be comfortable outside is way more than a jacket.