In the times of the dragon cult, Alduin was worshipped until the dragon-war. In the dragon-war Alduin stopped pursuing his destiny of destroying the world in favor of conquering it. So the Aedra intervened by giving humans the ability to shout, Akatosh intervened further by creating the first dragonborn. So Miraak became the best dragonslayer, but like Alduin he also chose a different path from his destiny and he didn't face Alduin in the final battle. Because of Miraak not fighting Alduin the time-wound occurs, forcing Akatosh to appoint another dragonborn in his place.

Did Akatosh appoint you in Skyrim as dragonborn due to him not choosing a worthy champion, or did he plan everything including the inevitable battle between the dragon borns?