I'm starting to wonder whether reactivity (not React specifically) was the originally sin that led to modern UI complexity. UI elements automatically reacting to data changes (as oppposed to components updating themselves by listening to events) was supposed to make things easier. But in reality, it introduced state as something distinct from both the UI and the data source (usually an API or a local cache). That int…
In my view, the problem isn't specifically reactivity but the fact that reactivity isn't actually native of the UI toolkit. Instead of HTML, think about GTK or Swing. To add React-style "reactivity" to it, instead of just making a dialog to change the "title" of a document and committing the change when you press OK, you'd need a top-level "App" class that holds all the state, a class for state properties with IDs ac…
And then said developer does what they think feels right: "I have my state and I simply want all the fields to reflect my state". So they try and rewrite the component into some sort of mini immediate-mode style component. All of the event handlers get wired up a single "layoutComponent" method that tries to call all the UI component setters based on the current state with all the problems you alluded to. I know I've done this type of things numerous times before going back all the way to my first internship, well before React was even a thing.
I think modern frameworks solve the reactivity issue this well enough, that it really doesn't matter if the underlying framework is not natively reactive. I will say though that I've primarily used Vue.js where most state is relatively local and we don't try to re-render the world on every input. I think part of the problem with modern dev is likely that React has become the default instead of a simpler framework like Vue.