Well, Napoleon kinda did usurp the ancient French throne.
Nope. He overthrew the Republic by a coup and the Pope himself took part in the coronation - he is as legitimated as any other monarch.
Yes, I know of the Brumaire Coup. But still, the French monarchy had been expelled from Paris and Napoleon ruled over France unlawfully.
How comes that the Pope took part in the coronation then? After all this legitimated Napoleon's rule in the name of god. All the other monarchs who took their power as granted by god ignored it out of personal interests, nothing more. The POPE legitimated his rule as well as the population, but the other European monarchs decided to ignore that. Napoleon's coronation was bigger then anything else seen at this time, he was 100% legitimated at this point.
After all there should be a coalition against the UK instead for sinking allied and neutral ships, but hey..... let's ignore facts.
(That's not meant salty, it is just meant to show the huge logical breaks happening in this game atm)