On the other side, there are many MacOS-specific features supported by Emacs, with the recently added dictation support being one of them. If a MacOS feature is missing, it's much more likely to be due to a lack of manpower than a desire to maintain feature parity with Linux.
The good news is that this fork was very competently maintained, so I had a good experience in Emacs on OS X.
The 2 or 3 times I tried "vanilla" Emacs (the one published on fsf.org) it had bugs that weren't present in Mitsuharu Emacs. One of those times vanilla Emacs did not work at all: it displayed a window, but the window was very small (i.e., incapable of displaying more than a few characters) and the usual ways of enlarging a windows on OS X had no effect. My (typing blindly) evalling (set-frame-parameter frame 'fullscreen 'maximized) also had no effect.
The homebrew package named "emacs" got you vanilla Emacs. To get Mitsuharu Emacs, you needed to install the homebrew package named "emacs-mac" instead.
Maybe vanilla Emacs got better on OS X during the past 4.5 years. I haven't had access to a Mac during that time.
Edit: I also remember hearing that for a long time an ffi was forbidden because someone could use it to call proprietary software. Don't have a source on that one though.