I'm afraid it depends on what standard this objective observer uses.

Here's a brief genealogy from Wikipedia. You can see that, if women are allowed to inherit claims to the throne, then Edward III of England is clearly the legitimate heir to his uncle Charles IV of France. But, the French argued that Isabella was completely disqualified by being a woman, and the succession must pass on as if she had never been born. If their claim was correct, then Philip VI was just as clearly the legitimate heir. The issue had never come up before, as far as I know, so either claim could be treated as legitimate at the time.

Of course, there are other standards that could be used aside from hereditary right. I'm not sure what result a plebiscite would have given, for instance - not that the idea of holding one entered into anyone's head at the time.