As the article mentions, the biggest problem by far with using mypy and the Python static typing ecosystem generally is the lack of third party support, even for big or new projects.

Python's benefits are as much about the libraries available as they are the language itself, and unfortunately it's kind of lacking right now especially compared to e.g. TypeScript support in npm.

Waiting for it to get better only goes so far; there isn't yet a cultural expectation around publishing typesheds for everything.