That is the license for the Android Open Source Project. Unfortunately, Google has spent the last fifteen years moving many parts of the stack and almost (if not) all the core apps to Google Proprietary versions. Most apps in AOSP no longer receive updates at all.
The dream is here is not just that we would be running "an open source stack" but that the active development would be on the open source stack. Sure, there are new releases of AOSP. But take a look at the core apps: Contacts, Calendar, Camera, Email, Location services. These are all proprietary now.
Android is open source in the same sort of way that MacOS is open source. There are some open source bits in there.
Who cares about the google user space apps? There are viable open source alternatives for all of them. It's like saying Linux is not open source because Redhat bundles proprietary software with their distro.
This could have been a reasonable analogy if a very significant chunk of applications "for Linux" only worked (or offered its full functionality) if you had Red Hat's proprietary addons installed.
That's just not true. You'll need to give a specific example of which apps are like this on Android. I'm writing this using a LineageOS phone with no proprietary or closed source apps on it right now.
This is true and can be verified by anyone by installing random applications from Google Play Store without having Google Play Services installed. Since relatively recently, you can use some of them via microG, but compatibility varies.
Sure, there's F-Droid and FLOSS software for Android, but if you're already willing to limit yourself to FLOSS Android apps you may very well limit yourself to FLOSS GNU/Linux apps too. When people say "I can't move to Linux phones because I need these Android apps", they usually aren't talking about ones from F-Droid.