If you're in the studio creating scenes, you aren't going to use your iPhone, so it doesn't really matter. If you're going to buy a camera to carry everywhere, you're still not going to use your iPhone. So it's really an academic theoretical issue, in my opinion.
Meanwhile, your DSLR is sitting at home in the closet. Guess which picture wins.
Here are two pictures I took recently, one with the iPhone, when the light was amazing, and one with my DSLR much later in the day, when the light sucked: https://goo.gl/photos/cnMFQaeUNHcBQdVG7
The clouds in the iPhone photo look amazing, and there are no cars in the street cluttering the view. But zoom in and see nothing but sensor noise and blurring from compression and generally poor technical performance of the camera.
Then look at the one taken with my DSLR. You can zoom in far down the street and read signs perfectly. But there is nothing interesting in the picture at all.
The iPhone phone camera sucked. The iPhone photo wins.
(Honestly, the iPhone camera almost ruins the picture, it would have looked amazing with the DSLR. But it was at home on my shelf. Not very useful there.)
Ever heard of medium format? (and there are other options too).
I find this modern preoccupation with crazy ISOs (which one would never use in the film era) a red herring. Especially for landscape work, it's a non issue. What you want there is excellent dynamic range, which those offers.
And there are some such as these that are quite the monster: Pentax 645Z.
And it'd be mostly irrelevant anyway, because it ignores all the other advantages of using a DSLR.
