I get where you're coming from - but in my experience, the barrier is totally psychological. Objective C isn't that unusual a language - the syntax is a bit foreign, but nothing that takes more than a couple of days to wrap your head around.
You'll spend far more time getting to grips with Cocoa/Cocoa Touch.
Lisps have the RPN psychological barrier. Python has the significant whitespace psychological barrier. etc. Any language can present someone with some psychological barrier.
I think the OP's strongest point was, Objective-C the language is pretty trivial to learn quickly (after all, it's just C with message passing). You'll spend far longer trying to learn the Cocoa APIs than you will spend learning Objective-C-the-language.
For instance, I decided to try to learn swift and SpriteKit at the same time. I spent far longer looking up methods on SKSpriteNode than I did looking up language constructs. (i.e. I assumed "let" was the same as in ES6 and couldn't figure out why the compiler was mad.)
Okay, I meant more that there's not a skills barrier in terms of actually learning to use the language. The syntax can be intimidating, but once you've spent a couple of hours with it, it's not an issue any more.
It's far more difficult to get to grips with how the APIs work.
@UIApplicationMain is the key there, from what I can see. An Objective C iOS app typically includes a main.m entry point which calls UIApplicationMain and passes the AppDelegate. This seems to have been removed in favour of what Swift is calling a "declaration attribute", which presumably does the same thing.
In this sense, the code is even less clear than the Objective C implementation.
You'll spend far more time getting to grips with Cocoa/Cocoa Touch.