I don't think this will do anything to help with the "crappy iPhone [app] ports to the iPad", at least not for a while. Those apps will still be there, and they'll likely still be approved in the future.

From my understanding, "iPadOS" is essentially just a marketing signal that the iPad-version of the OS will have more features unique to iPad. For developers, Xcode will still have the option to compile the same codebase for iOS and iPadOS. It's up to the developer to take advantage of more screen real estate when available, though SwiftUI will probably make that easier on the developer (i.e., more likely to show up in the apps you use).