And you can never mandate that optional type checking in a big enough team.

You can even see popular FOSS Python packages that have very limited type checking.

Why not? Have mypy/pyright/pryefly/ty type errors break CI. If you're starting a new project, there's no reason you shouldn't.

> Have mypy/pyright/pryefly/ty type errors break CI.

Only if types are present.

> If you're starting a new project, there's no reason you shouldn't. Most dependencies would still be untyped.