I suggest you re-read. This appears to be a flaw in iTunes, not iOS, where if the user is stupid enough to download an app from an unauthorized/untrusted site that knows how to do it, the app then exploited a feature in iTunes to make it a "trusted" source of apps and could proceed to download other apps without authorization.
That's not "owning" my phone, nor can your version of iTunes do that without you specifically targeting it. Worst case: you can install some crapware on my phone that I can simply delete. If I were idiotic enough to compromise my phone in the first place.
“if the user is stupid enough to download an app from an unauthorized/untrusted site “
Look up “Pro Tools Ilok problems” to see what happens when one vendor controls all the marbles.
Then see the result in tens of millions of dollars in damage, lost sales, closed businesses and broken contracts due to the Soviet model of computer security.