To be fair, this isn't like Amazon's "fire OS" where they just added a launcher app and randomly broke some APIs on accident. It's a pretty substantial addition to/departure from stock Android

Sorry yeah absolutely, I intended to frame it as they have effectively thrown out pretty much all of the Android UI/UX along with building an app store from scratch.

They were building a custom OS for VR/AR, but development of it was slashed earlier this year.