I have never owned an iPhone and even I find this a very bad idea. A lot of people buy iPhones because they prefer the choices made by Apple. If there were secondary AppStores, you would have a Metastore and a Googlestore very quickly, since Whatsapp and Google Maps have become indispensable for large parts of the world. You don't even have to take them off Apple store, but make newest features custom store only. The…
If you want the security of an all-Apple ecosystem, you will still be free to do so. If I want the freedom to install whatever I want to my iPhone, I will be free to do so.
Nobody is trying to take away your right to use your phone as you want, they are trying to grant you the right to use your phone as you want.