In other words, I'm not advocating large sprawling cities, nor am I advocating a return to rural population distribution, but rather saner sized cities.
That's medium?!
What do those cities have which a city of 100k inhabitants does not have?
Not to say that a city of 100k lacks any of these things, but a place far larger can have much more.
I've lived in a 100k city for a few years. It was a fun time, I liked it a lot, and you have access to most amenities, but you do notice it is a small city. Fewer different restaurants, very limited selection of bars and night clubs [1], much limited selection of cultural events.
[1] This has an unexpected upside: you can go out on a whim and expect to find your friends at the usual places, in a Cheers like fashion.
Not in Germany [1] (which is the topic here), nor in The Netherlands (where I'm from). Amsterdam doesn't have 1M, yet it is very culturally diverse. Zaanstad (containing Zaandam) is 'only' ~150k, and has the most cultures of The Netherlands (a total of 135 different nationalities).
[1] https://www.worldatlas.com/articles/the-biggest-cities-in-ge...
EDIT: Ah, now it makes sense. Thanks for clearing it up! :)