/second Nix on OSX. In addition to your reasons, it doesn't depend on the Mac community for growth and support as Homebrew and MacPorts do. Regardless how many OS X users use it, its bread and butter is NixOS and the Linux server community.
Sorry for missing Nix! I have almost zero experience with it outside of hearing that it existed, and MacPorts has been working fine for me, so I didn't go any further than that :( I'll have to try it out sometime; it's nice to know there are a couple of other options for macOS if I'm ever feeling underserved.
Getting started: https://medium.com/scientific-breakthrough-of-the-afternoon/...
How much effort was put into making the whole isolation: https://www.youtube.com/watch?v=73mnPBLL_20
There is even a declarative way to setup darwin process management: https://github.com/LnL7/nix-darwin