I'm enjoying iOS7 however there is definitely room for more improvement on it. The UI in some areas is too simple and too CLOSE together! Space between buttons is a good thing. I've read 7.1 makes some more UI improvments.
I won't argue PS's abilities, but it has had a 20+ yr head start in the pc graphics world. However, given what this app can do and for how small it is, says a good amount with its programming. Your other mention about Apple not unseating certain pro apps... I think Final Cut Pro is a good example of that. Granted they didn't invent it, but have been developing it since they bought the original piece of software. If memory serves.
The only thing I've noticed so far is the in the App Store app, and how it doesn't remove updated apps from its list once they are done. Anybody else notice this quirk? Im sure it will be addressed in a update, but not sure if it is an actual purposeful feature or not.