The situation is messy. Take Facebook.app. The reported size on the App Store is 377MB, the distributed .ipa is 241MB. But it is a universal app which includes fat binaries arm_v7 and arm64 and all the graphics 1x, 2x and 3x. App Thinning halves that size for end users. Yet the App Store reports the full size.
There's more. App Store also provides some sort of delta updates [1], which save a lot bandwidth, but failing to report it properly again [2].
App Thinning does not work for standalone image assets. It means you are forced to use Asset Catalogs where all PNG files are stored as LZFSE (previously zip) compressed BGRA bitmaps. It's good. But optimized PNG files can be 30-50% smaller on average. I'm fighting this [3] but not sure if there's a simple solution.
[1] https://developer.apple.com/library/content/qa/qa1779/_index...
I was wondering why not use SVG (or any other vector file format) files and render all the graphic on the device, instead of including tons of PNG at various resolutions.