upgrading your base image won’t affect your python packages
Surely if upgrading python will affect your global python packages it will also affect your venv python packages?
you can use multi stage builds to create drastically smaller final images
This can also be done without using venv’s, you just need to copy them to the location where global packages are installed.
Sure, but in the case where you upgrade python and it affects python packages it would affect global packages and a venv in the same way.