A back button would make no sense to me. There are situations in apps when you can't "go back" -- wait, do you mean some physical back button?! Otherwise, there's the "Return to..." feature, the fact that the back button in most iOS apps is always the top left button of the navigation bar, and there's always the left edge swipe. If you can't figure out how to go back in an app, then it's the app's fault, not the phone's. "I have to learn every single screen of every single app" -- come on, bro, that's a bit much.

As for the store, well, the App Store actually has standards and minimums for apps and reviews. I would think a google search for "best qrcode app ios" would yield better results than your strange method, but, hey, to each his own.