There's a weird meme I keep seeing that Vue does not scaling well that I've never understood. The state management is very easy to modularize and provides a very clear path to understanding what data goes where.
As for theming, it's trivial to import a master SASS file or 3rd party theme like Bulma and then overwrite where needed in components. Unfortunately my work chose to use Tailwind, so I don't get to reap those benefits.
My issues with React were almost always footguns, like with Redux and its middleware or the three or four ways to handle `onclick`.