Before uv, I was fairly happy with pyenv + venv + pip for development and pipx for running "tools". IMO, the specific things uv improves upon are:

  - Faster dependency resolution. In fact, everything uv does is extremely fast.
  - Better ergonomics in a dozen ways (`uv run` instead of activating the virtual env, support for script metadata to run scripts with dependencies, uv add to modify the pyproject.toml (that it created for you), etc.)
  - Stack of one tool instead of four+
  - Easier Python installation (although I usually use both pyenv and uv on my machine)