Android is not pure OSS and it's heavily tied to everything Google. Phones with custom ROMs are hardly available so it's far from being the ideal model.
The reason you don't get phones with custom ROMs is that those can't get a license for preloading Google Play Services, Google Play Store, Google Maps, etc., and without those nobody would buy the phone. The monopoly of the Google Play Store has allowed Google to keep a tight grip on the ecosystem of their "Open Source" OS.