Sorry, by "no standard tooling" I meant "no standard tooling" in the sense of no tooling in the standard Python distribution.

Seeing that mypy is under github.com/python/, you can easily argue that it is in fact the standard tool for type-checking python code.

And also that the second highest contributor is Guido van Rossum (https://github.com/python/mypy/graphs/contributors).

Fair enough, those are reasonable arguments the grandparents could (and should) have made.