Interesting, a cursory glance at the git repo for imposm3 looks promising. Which also lead me to https://mapproxy.org/ which the maintainers of imposm3 also created.

I understand your comment about sql thinking, in my day-to-day work I'm a bit of a reluctant sql developer (shudders in procedural spaghetti) but am gaining appreciation for being able to hand off aggregations and calculations to the db.