I use MacPorts, but I recall hearing the alternative Homebrew Emacs packages apply lots of patches onto the Emacs codebase itself and may cause stability issues. Users should be aware of this before deciding to use emacs-plus over the regular emacs package on Homebrew.
So rather than the install section being "out of date", I would say it is more conservative and may reduce the probability of users' first Emacs experience being buggy.
It has been my daily driver for a few years. I don't notice any instability. It appears to only apply 4 patches, includes lots of extra app icons, and the remainder is just setting sane default compile options.
Also it appears --cocoa is no longer a valid option even on the default HB emacs, so it is out of date anyway.
From upgrading today from 28.2 to 29.1 on my Intel 2019 Macbook Pro on Ventura, the macport one you linked felt snappier and far less stuttery than emacs-plus installed with the --with-native-comp flag enabled.
So rather than the install section being "out of date", I would say it is more conservative and may reduce the probability of users' first Emacs experience being buggy.