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

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.