I never coded native apps so forget my ignorance but how would you build an UI declaratively with swift? The turorial shows very imperative/mutative code indeed:

@IBAction func setDefaultLabelText(_ sender: UIButton) { mealNameLabel.text = "Default Text" }

No need to apologize for asking an honest question :)

By combining a good databinding framework and reactive extension

so Bond & RxSwift or DataBinding (from google) & RxJava (or RxKotlin if/when it becomes a thing).

Of course, behind the scenes, this accesses the platform widgets in an imperative way (but that's also what RN has to do when it manipulates the same widgets). What matters is the API surface you interact with.