I throttled it down to Chrome's "slow 3G" setting and it still worked fine. The filters were active as soon as the page displayed, though the images took a lot longer to load after that.
There might be cases where the issue you describe occurs, but I haven't actually seen it in testing. If it's a concern, you could of course add throbbers or the such. But generally, in our limited tests, it hasn't been an issue.
But again, the benefit is mostly to the developer experience. It's a lot easier to write everything in React than to have to switch between PHP and Drupal (as in the admin UI) and JS. There are some benefits to the user experience if done well, but the same could be said of a statically cached Drupal output.
There might be cases where the issue you describe occurs, but I haven't actually seen it in testing. If it's a concern, you could of course add throbbers or the such. But generally, in our limited tests, it hasn't been an issue.
Still, it is an issue they (and the React ecosystem) are actively working on improving, with React Suspense (https://17.reactjs.org/docs/concurrent-mode-suspense.html) and Next.js Layouts (which I understand is copied from Remix(?) and can fetch component groups in a hierarchy https://nextjs.org/blog/layouts-rfc). There is also server components and streaming, which can render HTTP snippets/components (instead of pages) and send those back over the wire, similar to the PHP days: https://nextjs.org/docs/advanced-features/react-18/streaming
But again, the benefit is mostly to the developer experience. It's a lot easier to write everything in React than to have to switch between PHP and Drupal (as in the admin UI) and JS. There are some benefits to the user experience if done well, but the same could be said of a statically cached Drupal output.