Well guess what, that’s a huge benefit for Lua because its entire total size is around 500 KB.

Filesize doesn't matter, if the functionality is missing. Lua is just not a direct comparison and replacement for Python. Penlight isn't standard library. In example if I want to write a commandline script, I better off doing it in Python. The language is much better to me, has better features, has a standard library builtin and is even installed in all Linux distributions.

Lua is meant to be embedded into other applications, not meant to be used on its own.

Lua’s problems with the absence of popular libraries aren’t because of any language issues (even the lack of null can be dealt with), but solely due to its non-adoption in the masses.

Wrong. This is a design choice, because Lua isn't meant to be used by its own. The embedded environment is meant to provide the functionality. In example in Neovim they provide their own functionality embedded within the editor. I can't use that script on a different environment.