I have the odd feeling that this kind of overestimation comes from the experience that folks tend to have in writing more traditional N-tier applications, especially post-Rails. A certain kind of database-first, ORM-first design philosophy really took hold after that, and it became somewhat common to see incredulity in response to telling someone that you weren't using something like MySQL or Postgres in production.

The kinds of projects that I more generally tend to see make these migrations successfully are the ones that design with in-memory data structures first and then sort out how best to persist that kind of thing to disk after their domain model has solidified a little bit.

Tailscale smells a lot like that to me.