There is plenty of evidence from Android that it would benefit both users and developers.

Android is not a model for this. Stores on Android simply don’t have equal footing with the play store.

Epic is suing Google too over this.

Epic is suing Google for pressuring OEMs against preinstalling its app store on devices, not for preventing users from installing its app store themselves. It's true that app stores not signed with the system key can't automatically update apps, and users would benefit even more if they could, but users already benefit from being able to install apps outside of the official app store at all.

You just confirmed my point.

Android app stores other than google play aren’t remotely on a level playing field with the Play store.

I never disputed your point (though it is technicall bwrong because some phones have other app stores installed on the system partition) because as I already pointed out, your point is irrelevant. The fact that users can install apps from other sources at all has massive benefit, as Android has already shown. There would be even more benefit if other apps could do automatic updates, but there is already benefit with what is available.