For that kind of thing I'd always either used the tagged Python images in Docker Hub or put the build step in an early layer that didn't have to re-run each time.
One other advantage is that you know the provenance of the python executable when you build it yourself. Uv downloads a prebuilt exe from https://gregoryszorc.com/docs/python-build-standalone/main/ who is a very reputable, trusted source, but it's not the official version from python.org. If you have very strict security requirements, that may be something to consider. If you use an OS other than Linux/Mac/Windows on x86/ARM, you'll have to build your own version. If you want to use readline instead of libedit, you'll have to build your own version.
I am personally fine with those limitations. All of the OSes I regularly use are covered. I'm satisfied with the indygreg source security. The libedit version works fine for me. I like that I can have a new Python version a couple seconds after asking for uv. There are still plenty of reasons why you might want to use pyenv to build it yourself.
