If anything, you are being too nice to US suburbs: It's perfectly possible to have towns that are much denser than any US suburb. My Spanish home town has about 100K inhabitants: You'd not call that a city anywhere in the US. And yet, It's basically a circle with a one mile radius: Yes, just one mile. In that situation, one can walk everywhere, and public transportation is limited to the elderly, people carrying heavy things, and the impatient that live in the outskirts of town.

As a pre-teen, I could go to any of my friend's houses to do tabletop roleplaying all by myself. If my mother needed a break from parenting, she had three different siblings living within a quarter mile. When your average building is 6 stories tall, and your typical street is 30 feet wide building to building, a quarter mile circle holds a lot of families! In comparison, my neighbor from across the street in the US suburbs is 60 feet away, door to door, and a quarter mile circle won't get me to 300 front doors, total.