React absolutely improved things from spaghetti jQuery. The zero-to-one productivity for interactive UIs goes through the roof, but growing and maintaining your project for any serious business use case is a complete nightmare.
I don't wish isometric javascript on any one. Javascript was infamously created in a week or whatever and now it's the browser standard, so be it, by why in god's name would you ever pick it for your server?
I burned myself out working on a personal project completely on my own using nextjs. I was super productive at the start, then as business logic increased... typing and flowing everything through components, state, reducers, selectors, async network calls, good God I grew to hate all of it.
I came crawling back to Rails. Everything and the kitchen sink is loaded in a controlled and blocking env. You can abuse the fuck out of it and it smiles at you. I'm sorry I left you Rails. (rails backend for all business logic: "the brain". Thin/dumb React JS client that consumes view-based APIs. React is great for interactive UIs. Not your fledgling business logic)
The majority of the complexity is in the ancillary tools and ecosystem extras, which are not strictly necessary. You don't need bundlers and transpilers, for example. The only reason they are popular is because JSX is a good convenience, though.
You can get away with very basic React for the majority of cases. Things like advanced lifecycle shenanigans are also not necessary, unless you’re doing something extra-smart, or inherently complex (due to browser APIs, third-party APIs, or just complex design patterns). But those are also not necessary: just nip complexity in the bud if possible, but if something becomes impossible to avoid, the complex side of React will have your back.
The main difference between jQuery and React-the-library is that React handles a lot of the complexity around state and component abstraction all by itself.
With jQuery the complexity and spaghetti appears much earlier than in React. It's even difficult to compare, it is much simpler to keep a React codebase cleaner than a jQuery one.
Of course, if your app is simple enough, you don't need the "extra complexity" brought in by React, and jQuery will serve you well.
But this is also true even for "simpler things" like jQuery and Ajax: if your app is simple enough, you don't need Javascript at all, you can handle 100% with server rendering. And so on.
Web apps can reach the complexity of a desktop app with a GUI, a game, etc.
I say this as a mostly backend / systems engineer: there is an incredible wealth of complexity in the frontend. In user interaction, making and transforming API calls, and in UI/UX design.
the moment you have to keep track of any type of state, managing dozens of UI elements quickly becomes extremely tedious.
Actual React apps are as simple and elegant as a complex (web) application ever could be. Separating your app into functional components where most complexity is always local is a great way to make the application structure as simple as they can be. Where developers often go wrong, is trying to force patterns from other frameworks or languages into React and TS/JS.
I think if more people would do this exercise they would find that they don't need it, or at least that they might need some form of state reconciliation, but not enough to really warrant all the complexity the tool introduces. Some will find that they don't need it but will still use it for other reasons, like familiarity or because that's what their team uses.
If the developers have experience with other languages and native UI frameworks then they probably won't want to use any of the Javascript frameworks when developing a web application as they already have a mental model for how to setup the structure of function callbacks for handling user interactions and state changes.
This is exceedingly complex, error prone (because you might miss parts of the state that should change) and often slow (because you tend to overcorrect).
It does require a lot of thinking before hand about the user interactions and their impact on the application state, user workflows, etc. However that thinking should already be happening regardless of the choice of implementing technology (granted it doesn't in a lot of cases :| )