What are the downsides? Benefits are if you use something that uses Pydantic models (say, fastapi + sqlalchemy) for example you seem to be able to get more granular control over DB types than, in my recent experience anyway, we had using Prisma / Nextjs.

We switched over, have fastapi generate an openapi.json, then use Kubb to have it auto-generate typescript types (it can also do zod models), done.