The non Google Play stores are severely nerfed though - they for example can't auto-update apps installed from them, like Google Play can.

So if you install something say from Fdroid and want to have it up to date (say a Firefox rebuild), you have to periodically open the Fdroid app, check if there are any updates for the app and manually install them if there are some.

Also I don't think you can currently hide Google Play if its installed, again giving it an unfair advantage.

This is probably because I'm running a Samsung os, but I get auto updates from the Samsung store.

The vendor has custom modules for auto-updating. afaik F-Droid also auto-updates on freer distributions of Android but not on most manufacturer ones.

Exactly. This is because F-Droid requires root access to provide this functionality. I'm not sure if the module for this is still up to date, but it is a Magisk module that could be installed on any Android device rooted with Magisk.

Well I actually also have a Note 9 and it seems Samsung stuff generally does not get updated by itself & either stays outdated or nags for update I need to manually trigger.

Stores that are baked into vendor images are granted special privileges to act as app stores.

It's not quite that dire, as F-Droid will pop up a notification when there are apps that need updating. But yeah, you do have to tap through and confirm to get it to update, once for each app.

It is a feature, not a bug. Moreover, I want to be able to roll back the update or install an older version and pin it.

I think having two app stores being installed would (or should) satisfy this.

I think the intention is to prevent Apple saying "either you use our store exclusively, or you opt out of all our apps".

Google lets you install a browser from one store, a game from another, and everything else from the official Play Store.

Google could also easily implement category switching. The URL navigation structure of android could just append ?cat=gaming.