Google could absolutely close-source enough of Android to make it essentially closed.

As I posted elsewhere:

Couldn't Google have had Samsung OEM phones?

With co-branding?

And all of the profits going to Samsung?

This would merely be a different way to structure access to Android, right? Android is closed source, but literally everything else is the same...

Except now it's not "anti-competitive," because the phone manufacturers are not "competitors" to Google.