- There are a thousand ways to render HTML, you don't need React at all. Even for interactive pages (see recent alternatives like HTMX, or decade old solutions...)
- If it is converted to JS/React it's obviously not "pure" Python. Sorry, but that's just silly to say that.
- You will definitely see JavaScript errors during runtime, it's inevitable. Maybe not with simple toy projects, but with serious projects, it will happen and will make life miserable.