No, sorry if this sounds rough, but it's a 'not even wrong' comparison - the UI component code for Android is open and in the 95% case, _not_ tied to an OS version. What you're referring to as closed source and proprietary APIs is the idea that APIs backed by a Google service (ex. GPS coordinates -> address) are shimmed out and require a plugin from the vendor - and ex. Google's version of this API is _not_ open source, and the open source version of Pixel excludes non-Google elements (such as the date + weather widget not having weather)
>Play Services is a closed source app owned by Google and licensed as part of the Google Apps package. Any feature you see move from "normal" Android to Google Play Services is also moving from open source to closed source. This app pulls off the neat trick of not only enticing users with exclusive, closed source features, but locking in third-party developers with Google's proprietary APIs as well.
Yeah, the language you quoted is histrionical and responsible for innumerable mistaken impressions, including me, until last year. If you skim the headings you'll see it's things that'd more or less be 'obviously' proprietary - headings include Google Maps API, in app purchases, Play Games saving/scores...
As someone who's spent just as much time (if not more) developing for embedded Android devices without Google Play Services as developing for "traditional" ones, you're making a meaningless distinction.
It's half the functionality that makes an Android device work for an unsophisticated user. To the point that people have to write shims just to get basic apps to run without it.
And the amount of functionality Google has moved into GPS has only grown over the years mind you, from things like Doze and its interaction with GPS, to installation processes that hook into it for verification...
If Android didn't have Google Play Services, it wouldn't be anything more than what Linux on smartphones is... a toy for geeks, nothing competitive with offerings like the iPhone.
