I just finished up FFXV and I feel partially satisfied and partially confused. At first glance Ardyn is a great villain with relatable motives but the more I thought about it the less it makes sense to me. Can anyone clear up my questions?

1) If Ardyn was chosen by the Astrals to clear up the Starscourge then why, once he'd completed his task, was he banished from ascending by the very same people who tasked him? That makes no sense to me. I get that the king banished him and stole his name because he was jealous of his feats but the Astrals just seem contradictive and dickish in their logic there.

2) If Ardyn was never a king or a royal and his name was simply stolen via the king at that time then why can Ardyn use the Armiger, the royal arms and all of the warping abilities supposedly only available to the royal family of Lucis?

3) Who's surname did Ardyn steal? He states 'You'll never guess where I got Izunia from' and I've been trying to think who but nothing blatently obvious comes to mind. The most obvious answer is that Izunia was the kings name who banished him.

Much appreciated guys!