The core of Boston is more walkable than SF is. Especially if by "walkable," you really mean walkable and with easy access to expansive public transit to easily get to all the other things you won't have in a small town center or otherwise within a 30 minute or so walk.

To the sibling comment, walkable means different things to different people.

Walk to a hospital or a grocery store that isn't a small market/convenience store? You're already talking a city at that point. And, in the hospital case, probably not all the medical professionals you might conceivably want to see are likely to be within a one mile or so radius.

A ton of places are walkable in the sense that you can buy a house/condo and walk to a restaurant or two and pick up a few groceries. But, as you say, very few cities in the US are walkable in the sense that you really don't need a car without a lot of compromises/depending on others/using personal transportation services a lot.