I'm not against your idea of viewing both the same, but in your post, there are many loose pointers, let me list a few here:
* You mention creating of RESTful API like it's a walk in the park.
* You take 2-5 days to create the flow of app and jump from mockups straight to testflight!?
* You have a visual designer to implement your app?!
Fair enough, that you mention the loose points. From your article I got the impression that you think app development can be only be done as a waterfall project because of the toolset. And the point I was trying to make in my post is that my experience tells me otherwise.
Maybe my text was not clear on this. I will check it again.
To answer your questions: a RESTful API to be used by my app only and not to be consumed by the rest of the world is not such a big deal. Using the mock-up as input I'll create a working prototype in xcode in 2-5 days. After that I'll send it to the customer as soon as possible. The visual designer will design the app. I will implement the design.
As software engineers we are hired by our clients because we have knowledge and skills that they don't have. It is our job to educate them on the important parts. Always have, always will be. I understand your frustration, but it is nothing new. Or maybe it's just me getting old :-)