I'm fully in favor of replacing shell scripts with Python3 scripts wherever possible. In fact that's part of my job. That being said, the author of this article is using confusing / wrong terminology to discuss bash.
This article says that, "The [bash] shell isn't a complete programming language". While I agree that bash lacks any real data types besides strings, bash is a Turing-complete programming language[1], so it's theoretically possible to write _any_ program in bash that can be written in Python. It might be a hell of a lot uglier and lack things like imports, modules, etc., but it can be done.
For example, there is an implementation of an HTTP daemon written purely in bash[2]. Once again-- terrible idea, but great execution.
[1]: https://en.wikibooks.org/wiki/Bash_Shell_Scripting#A_few_not...
[2]: https://github.com/avleen/bashttpd
edit: added newline to separate references
It's not pure bash, as it relies on netcat or socat plus some other external programs (ls, tree, cat, date).
There does exist a pure bash httpd though. It relies on a loadable builtin (from the bash tree though not built by default).