To the extend that Python is indeed "batteries included," that seems true. But just how "batteries included" is it? I'd argue that its batteries are pretty limited. Exhibit A: everybody uses the third-party requests instead of the stdlib urllib. Exhibit B: http.server isn't a production-ready webserver, so people use Flask or something beefier.
I'd contrast Python with Go, which has an amazing stdlib for the domains that Go targets. This last part is key--Go has a more focused scope than Python, and that makes it easier for its stdlib to succeed.
We could have different Python package bundles: Python base. Python webdev. Python desktop.
> http.server isn't a production-ready webserver, so people use Flask [...]
Nit, but relevant nit: Flask is also not a production-grade webserver. You could say it is also missing batteries ... and those batteries are often missing batteries too. Which is why you don't deploy flask, you deploy flask on top of gunicorn on top of nginx. It's missing batteries all the way down (or at least 3 levels down).