> I recall you used to be able to flip some bit somewhere to allow you to Quit the Finder

you can still do this with a hidden preference using command line:

  defaults write com.apple.finder QuitMenuItem -bool true; killall Finder

[0] https://www.defaults-write.com/adding-quit-option-to-os-x-fi...

  > But even then, you'd want more than just that, as when you tell the OS to "Reveal" a file or open a folder, that's the association I'd want to be able to change.

yep, that should just be a normal setting like default browser (one thing i like about linux nowadays)