This is the exact problem I have. No bash scripting tutorial would tell you to not use your system bash. No perl tutorial would tell you to avoid your system perl. No C tutorial would discourage using your system's gcc or clang.
As I said, a lot of the value I see in python is in its ubiquity. This disappears if you can't use the system python.
You can always use the system python to create a venv. It's ubiquitous in the sense that you don't need root access to use properly, not that it comes set-up and ready to use for all purposes.
There's the risk of breaking the system when using system python. Install some dependency for your script that changes something that a core service is depending on in an unexpected way can lead to hours of tracking down the issue. Or a full reinstall in the extreme. That's why users are to avoid using system python.
But if you value that ubiquity more than your sanity, I hope you find and fix any breakage yourself and not pester other devs for support.
As I said, a lot of the value I see in python is in its ubiquity. This disappears if you can't use the system python.