I haven’t ever seen issues scaling with jotai even on very large apps working with extremely complex data structures.

I’ve seen far larger messes created in redux due to tight coupling of things across large apps to a global store and the inability to work with things like Maps and Sets or other values that are not trivially JSON serializable.

In the other direction I have seen messes with observable-based state management systems where things become far more complex and too far abstracted (how often do you really care about anything other than the latest value and maybe the previous one?) or with proxy based systems that have too much fragile magic (valtio, mobx) or require wrapping your components and going all in on oop (mobx)

To me signals hit the magic spot of reactive without being overkill and keep code testable in smaller units while retaining performance benefits of surgical updates

I like xstate in theory — it’s a good way to think about complex state transitions — but in at least half of cases in practice where you aren’t interested in a derived value, someone is storing a value/ getting the latest value or toggling a boolean and it’s just such overkill for that. The reducer pattern itself doesn’t meaningfully show up much for similar reasons. The other common cases are with fetching states (idle, loading, refetching, success, error) but you often end up wanting things like cache management or maybe even optimistic updates so eventually tanstack query covers that ground better than rolling your own.