I'm curious. The homebrew formula seems to just download emacs from the main GNU repository. So what makes emacsformacosx better? The website doesn't seem to explain this.
One thing it gives you out of the box that is difficult with the other Homebrew options (there is also https://bitbucket.org/mituharu/emacs-mac/overview) is a standard macOS application that you can launch with Spotlight.
If I remember correctly, one of the developers of GNU Emacs removed Mac-specific functionality as GNU doesn't want these type of patches in the software that they release as it goes against their core ethos.