>> I've noticed React is often conflated with the wider ecosystem it is a part of (Webpack, Redux, Babel) - perhaps this is the complexity you are referring to, but to be clear React can be used without any of these things.

I disagree with this. Everyone claims that you can use React without JSX but no one does it. Aside from ugliness, the main reason why no ones does this is because you would be missing the most useful aspect of React which is compatibility and consistency with the rest of the React ecosystem. So you cannot separate React from its ecosystem. All this complexity has become tightly intertwined.

If you use VueJS without a bundler (which is actually feasible), you will be surprised how much simpler and elegant the whole development experience is. Once HTTP servers start supporting static push of scripts, we will not even need bundling in production.