There's also Epic Games who distribute Fortnite through their own Android app store, and it sounds like that's worked out for them. Amazon AppStore can be installed on Android devices, and Samsung has their own app store too.
There are even big companies distributing Android apps directly via downloaded APK - gambling apps aren't allowed on Google Play, but Sportsbet in Australia still did a splashy TV campaign for their Android app APK:
On Android, you can distribute, download, and install .apk files outside of the Play Store [1]. There's also an app called f-droid [2] which acts as a 'store' for some open source apps.
[1] https://developer.android.com/distribute/marketing-tools/alt... [2] https://f-droid.org/en/