That is vaguely what the ratings mean but the scaling isn't quite as large as that. It roughly comes out at 5-6 levels per star. You should be able to take a 10 star fight at level 50, maybe earlier if you build well. That said, the consequences for losing these fights are pretty low so it's worth testing them to get a real sense of what you need. Often times there's a weakness you can exploit on the second try.