"(and by proxy, Android, thanks to the Google Play Store monopoly on app distribution) have seemingly permanently tipped the scales towards iOS at this point."

Do you even know what you are talking about? On an Android phone you could install other App stores and side load apps. You can't do any of this on iOS.

I think the argument is that app distribution is controlled by Apple on iOS and by Google on Android, and GP is happier ceding control to the former but not so much the latter. As Google Play Services become more entrenched in the basic functioning of the OS and apps on the platform, it becomes harder to extricate Google out of the Android experience, even if one has the ability to use other app stores.

I think it's a very reasonable position.

exactly, recently android was developed in a way that it's impossible to disable some core services which are directly associated with google services, so AOSP as such is almost impossible to exist separately from google.

You can side load apps to which you have the source code on iOS, for free.