Sure, these tools don't do much more fancy than that. The early days of pyenv was "just" a tool that output a Bash script that set PATH and PYTHONPATH and a few other environment variables.

There's still some utility in automating changing your PATH when you switch between projects: do you need to support multiple shells with different syntaxes for changing environment variables? Do you need to synchronize those shells sometimes? Do you need to change PATH for random combinations of multiple tools at once? Do you want to have a tool verify for you that you are changing PATH to refer to a version currently installed? And maybe automate installing it if isn't?

This particular tool supports a half-dozen different shells (on Windows) and a single file to setup PATH (and other environment variable changes) for any number and combination of tools all at the same time.

If you are happy with your manual PATH changes today and don't see a reason to automate them, then you might not need a tool to automate them. If you find yourself changing PATH a lot more frequently and hoping to automate it more, there are tools for that. As with anything, automation is a spectrum and what you might not do enough to automate someone else might do a lot more often than you and could use some form of automation to speed things up and/or catch easy or dumb mistakes.