> Coming to a FastAPI app with alembic and finding a lot of that is build-it-yourself (and easily break it) is a bit of a shock.

I briefly played with FastAPI, and after the same shock I discovered Django-Ninja [1]. It's modeled after FastAPI and async-capable (if you are inclined, but warning, there be dragons). It plays nicely with all parts of Django, including the ORM.

[1] https://django-ninja.dev/