Today i had quite too much free time in my hands, so i went on the Imperial Library to read some books, and i read a lot about Alduin being Akatosh. This is also supported by small hints in the game, such as Maiq the Liar. However, according to my researches, i guess it's the opposite: the Cyrodillic cult of Akatosh derives from the Nordic cult of Alduin. First off, Akatosh is the dragon (!) god of Time. Alduin is referred to as the World-Eater, he who created the world in the mythic time and will end it at the end of history. Second, and most important, Akatosh is an Aedra, and the Aedra make no appearance at all in mortal's world, unlike Daedra, which have artifacts and can be summoned. Alduin, instead, is phisically present in Skyrim. You may say Akatosh beats Dagon in Oblivion, but i think that may in fact be Alduin: in Skyrim, the only dremora found [<- may be wrong on this one] are on Dagon's shrine, and if you fight Alduin in the Throat of the World with a full set of Daedric Armor, he'll say "Even the Daedra fear me", probably referring to him defeating Dagon. This is what i came up with in my personal researches, what do you think?