Let's break that down across everything those 16k software engineers are responsible for:
• The OS kernels, drivers, and frameworks of macOS, iOS, watchOS, and tvOS
• The base-system software on all of those OSes, including rather involved apps like: iBooks, Safari, Mail.app, iTunes, Photos.app
• "Apps by Apple" like iWork, GarageBand, Pages/Keynote/Numbers, Final Cut Pro, Logic Pro X, iBooks Author, and, yes, Xcode
• Server.app (which adds to macOS the kind of enterprise domain-management + provisioning + MDM tooling that Windows gets in its Server releases, but also includes extra stuff like Wiki software, Xcode build-bots, and VPN management)
• Firmware + macOS drivers + Windows drivers(!) for Apple hardware (keyboards, mice, touchpads, headphones; I bought one of those MacBook USB-C multiport dongles recently and it did a firmware update, so apparently it has firmware too)
• Firmware and operating systems (usually NetBSD-derived) for "appliances" like the Airport/Time Capsule [though at least this has been dropped]
• Sponsored work on open-source projects (Webkit and LLVM being the two big ones) and standards (the Swift language; the Bonjour protocol)
• iCloud backend services: this includes the "obvious" things like the object store behind iCloud Drive and the per-app iCloud CoreData syncing servers; but also includes:
• • Apple's own maps service to back Maps.app
• • the iTunes store and App store (both in web and app form)
• • the Apple Music / "iTunes in the Cloud" sync servers
• • iCloud PIM support (mail, notes, calendars, reminders)
• • the FaceTime and Messages.app servers
• • Siri and Dictation (and you likely won't believe just how many languages Apple has built well-trained speech models for)
• • the Apple website / Apple Store + Apple Support apps
• • Xcode "development team provisioning" servers
• • webapp versions of iWork and the PIM apps (go look at icloud.com)
This looks like a reasonable list, however I think the overarching view is that with all of Apple resources (money, etc.) they should be able to point some of them at XCode. This may involve hiring developers or shifting priorities from other projects. Either way, it's something that most developers feel is necessary and good.
Then again, maybe this is another way of saying that Apple really doesn't care about professional programmers and their needs. Similar to the feedback around the latest MacBook Pro specifications and the lack of movement in the Mac Pro and Mac Mini machines.
Let's break that down across everything those 16k software engineers are responsible for:
• The OS kernels, drivers, and frameworks of macOS, iOS, watchOS, and tvOS
• The base-system software on all of those OSes, including rather involved apps like: iBooks, Safari, Mail.app, iTunes, Photos.app
• "Apps by Apple" like iWork, GarageBand, Pages/Keynote/Numbers, Final Cut Pro, Logic Pro X, iBooks Author, and, yes, Xcode
• Server.app (which adds to macOS the kind of enterprise domain-management + provisioning + MDM tooling that Windows gets in its Server releases, but also includes extra stuff like Wiki software, Xcode build-bots, and VPN management)
• Firmware + macOS drivers + Windows drivers(!) for Apple hardware (keyboards, mice, touchpads, headphones; I bought one of those MacBook USB-C multiport dongles recently and it did a firmware update, so apparently it has firmware too)
• Firmware and operating systems (usually NetBSD-derived) for "appliances" like the Airport/Time Capsule [though at least this has been dropped]
• Sponsored work on open-source projects (Webkit and LLVM being the two big ones) and standards (the Swift language; the Bonjour protocol)
• iCloud backend services: this includes the "obvious" things like the object store behind iCloud Drive and the per-app iCloud CoreData syncing servers; but also includes:
• • Apple's own maps service to back Maps.app
• • the iTunes store and App store (both in web and app form)
• • the Apple Music / "iTunes in the Cloud" sync servers
• • iCloud PIM support (mail, notes, calendars, reminders)
• • the FaceTime and Messages.app servers
• • Siri and Dictation (and you likely won't believe just how many languages Apple has built well-trained speech models for)
• • the Apple website / Apple Store + Apple Support apps
• • Xcode "development team provisioning" servers
• • webapp versions of iWork and the PIM apps (go look at icloud.com)
• • the Game Center servers
• • the iAd servers