Unfortunately, Python CLI startup time is correlated with how many files the interpreter has to interpret, which usually takes effort to combat, so larger CLIs that have a lot of functionality and thus files always seem to slow down.
The Azure CLI is a good example of this. It's been a year or two since I used it, so maybe it's improved since then, but it used to take a second or two just to run `az --help`, which infuriated me.
If you own a slow Python CLI, look into lazily importing libraries instead of unconditionally importing at the top of each Python file. I've seen that help a lot for slow Python CLIs at $DAYJOB
I generally say that anything under 500ms is good for commands that aren't crunching data, and even Python CLI tools can come in under that number without too much effort.