It would have make more sense for Arkay was once mortal, because that is the very thing he represents: Birth and Death, or in short - mortality. He's definitely not more powerful than Akatosh, because at the end of time isn't death, it's nothingness, and it's our divine father domain: Sithis
Doesn't Paarthurnax literally name Alduin "Akatosh's firstborn"? Like, the first non-god dragon made by Akatosh? In that aspect, Alduin is more of a demi-god.
But Alduin himself says ''But i am A L D U I N, firstborn of the Akatosh" so technically isn't Alduin the son of Akatosh and Akatosh the father of all dragon's, like they're different characters right?
Thank you! I’ve always been a bit confused about the Divines, mainly because I didn’t know their other names, I didn’t know Akatosh was the same being as Ari-el or Kynareth was the same the same person as Kyne (now that I re-read that it’s kind of obvious), maybe I’m just stupid lol but those specific details are really good to know