> and related content
That is a very interesting if not a prodigiously strained hand-wave of a solution to GGP's complaint, "that the OS has no way to keep apps up to date," as Safari, Mail, Contacts, Calendar, Maps, Music, Photos, Messages, FaceTime, Notes, Preview, TextEdit, KeyNote, Pages, Numbers, GarageBand, Quicktime Player, Activity Monitor, Terminal, Console, Disk Utility, and hundreds of other bundled applications, and including the tens of thousands of BSD userland utilities, as well as the AppStore itself, are packages managed by the package manager called Software Update, a Preference Panel in System Preferences, which is the GUI front end for /usr/bin/softwareupdate.
There is no package manager that exists on any platform that manages every application there is, but between softwareupdate, AppStore, and the only professional and stable third party package manager for macOS that exists, MacPorts —these three package managers can be employed to keep well over 2 million distinct installed packages up to date.