> different version of Android on each phone (with the apps replaced) No, their action actually lead to this in the first place — previously, each manufacture

> different version of Android on each phone (with the apps replaced) No, their action actually lead to this in the first place — previously, each manufacturer slightly modified the AOSP apps, now each manufacturer actually builds their entirely custom apps for this purpose, as most can’t or don’t want to license Google’s apps for that purpose (they license the base Google Play apps, but e.g. not messages or the phone app or the launcher).