There are way more downsides than that. 1. No recursive types, so you can't express a lot of basic things like a "Json" type. This ends up coming up a lot more

There are way more downsides than that. 1. No recursive types, so you can't express a lot of basic things like a "Json" type. This ends up coming up a lot more than you might imagine. 2. Not great support for every pep ie: Protocol 3. Generics are extremely confusing in mypy. Generic classes suffer from the lack of recursive types I'd mentioned as well. 4. Implicit 'Any' everywhere unless you use the strictest settings, which I don't believe anyone does on real code because of the above issues. I've never once managed to get a real codebase to typecheck with mypy. Honestly mypy works as a somewhat fancy linter, not as a type checker.