1. Only because Google might also engages in anti-competitive practices doesn't mean that Apple is allowed to. All such behaviour needs to be curbed.

2. Anyone can install any 3rd party app on an Android device, there's even a open app store "F-Droid" for open apps that anyone can use.

3. You can still run an app store. You just have to allow other ways to install apps. That way your store would be used only if it's better than the other ways to install apps.