It's always going to be slower than using something imperative. Trying to process the entire world's state for the sake of purity can feel elegant but it isn't free. And the complexity that gets added to make things performant is worse than just accepting that UIs are going to require you to jump around the tree and modify state.
Every time I go through the trouble of understanding the latest web technique (React, Elm, Signals (the newest solution), etc.) to deal with state management and the DOM, I end up walking away disappointed. There's nothing new in them that you can use to improve what we've been doing for ages in native GUI toolkits.
And to jump back to the original topic, yes, Cocoa was pretty decent, and SwiftUI while nice in many ways tries to Reactify native macOS development and made it worse. And it made Swift incredibly more complex and worse in hindsight.
1. The UI tells the model to change.
2. The model does the change and possible related changes.
3. The model notifies the UI that something has changed.
4. The UI updates itself from the model.
Alas almost nobody does MVC, despite calling what they do MVC.
I didn't say that.
User interfaces representation are mostly trees. And with functional programming you basically have Tree2 = f(Tree1). Until f is done you can't do anything really. React has a lot of escape hatches to improve performance, but they are escape hatches, not an endorsement of the architecture.
With imperative programming (and OOP), you only have that single `Tree`, which you update at will. Less elegant yes, but we have modularization to help us there. What Emacs does is to keep that `Tree` as a single mutable object, but have the code be functional, while the results are imperative.