Yeah strong typing is essential. Redux is overkill for small or even medium apps but it's the best tool I've found for dealing with the complexity of larger apps. Having a very clear, inspectable sequence of mutations to all your data becomes very valuable.

even with completion it's a lot of busywork: define actions, reducers, etc for every state change

If you use TypeScript and Thunk, it’s no more work than writing your own state management code on plain JS/TS objects. But you get all the advantages of Redux (dev tools, introspection, replayability, easy persistence and tab sync, etc).

You're probably right about Elm which is basically one big reducer, but Redux adds a whole lot more indirection on top of that which makes it much more complicated.

Even small Redux apps can start off with a lot of indirection as soon as they extract logic into selectors. This is probably the first area where Redux becomes more complex that what you were doing before:

https://redux.js.org/usage/deriving-data-selectors

It reminds me of reading a bunch of parser combinators: it feels like you're reading code that builds something that does what you want instead of the code that just does what you want.

    const makeSelectItemsByCategory = () => {
      const selectItemsByCategory = createSelector(
        [state => state.items, (state, category) => category],
        (items, category) => items.filter(item => item.category === category)
      )
      return selectItemsByCategory
    }

Yeah, with Elm, when you handle an event, you either update the model (state) or you generate new events. You don't have this selector thing.