There's still no native supplied SVG renderer outside of a web view, which makes developers more conservative. Apple's current advocated solution is to produce your assets as PDFs, after which Xcode renders them to the appropriate size classes at build time.
For iOS 11 onwards, there are two size classes, as there are no @1x 64-bit devices.
It's unclear exactly to what this article refers, but Apple's App Store uses a process called 'app thinning' to deliver to each device only the assets that device will use. So a 56mb upload is rarely a 56mb download. Or, if they genuinely mean a 56mb download, then that should vary.