I've been working on several third-party apps from iOS 4 to 10. Flat design (as implemented in iOS 7) hasn't really made development easier. Most iOS 6 apps weren't even crazy about textured backgrounds [1] [2] [3]. Mostly it boiled down to designers giving us a PSD that we would slice into handful of resizable textures for UI controls (like Android nine-patches). It was a bit like table-based HTML design, but in a good way, as the framework completely supported it.
Then iOS 7 killed textures, but introduced translucency to make up for its overall blandness. And that really ruined the simplistic beauty of UIKit programming, since everything now has to deal with all the band-aid that is needed to make views extend below translucent bars (layout guides, edgesForExtendedLayout, automaticallyAdjustsScrollViewInsets, ...). Here's a random example of how translucent vs. opaque bars can cause trouble. [4] We've traded a few minutes in Photoshop for hours of wrestling with UIKit's undocumented heuristics when it comes to layout code/transitions.
Then iOS 7 killed textures, but introduced translucency to make up for its overall blandness. And that really ruined the simplistic beauty of UIKit programming, since everything now has to deal with all the band-aid that is needed to make views extend below translucent bars (layout guides, edgesForExtendedLayout, automaticallyAdjustsScrollViewInsets, ...). Here's a random example of how translucent vs. opaque bars can cause trouble. [4] We've traded a few minutes in Photoshop for hours of wrestling with UIKit's undocumented heuristics when it comes to layout code/transitions.
[1] http://www.iclarified.com/images/news/24614/92620/92620.jpg [2] http://photos2.insidercdn.com/javascript-121220.jpg [3] https://cdn.cultofmac.com/wp-content/uploads/2012/09/Screen-... [4] https://stackoverflow.com/a/33537188