The commodification argument. People have been saying the iPhone is good enough for a decade so far (in fact from before it even came out) and there's no sign of their losing their grip on the high end of the market. In fact this has been said generally about Apple computers since the 80s at least. Hence Apple's unofficial corporate slogan, "Proudly going out of business since 1976".
The fact is nobody even tries to do the level of integration between software and hardware that Apple does. It's hard to compete with an opponent when you don't understand what they are doing, or why they are doing it, or why it works and it's very clear their competitors don't understand any of those things.
As long as the competition sit on their hands following the 'theoretically' ideal business 101 commodification strategy, which hasn't worked for 40 years now, it will continue to not work. But here we are, generations of business managers at Apple's competitors have come and gone and the wait them out strategy keeps losing.