Each time is a little different. It's not "besting Alduin" that matters, it's the attempt, standing between Alduin/Akatosh and uncreation. I cannot and never will attempt without permission to speak for 'we" but I certainly believe that in the end the Dragonborn has done so, even if only for that time a-la Cyrus Hoon Ding Redguard.
Standing against Alduin, Shor's deed, as the original Alduin is meaningless in a myth without Shor, other myths have their own dragon ascpects.
Standing against Alduin, Akatosh's deed, as Alduin brings end of time and Akatosh is time of present, and to King Akatosh Alduin is playing the Rebel as Alduin wants to become the King.
Standing against creation-reversing, Talos' deed, as Talos is the one that bound Mundus to the hub of Wheel and fortifies Mundus.
And Alduin doesn't equal to creation reversing, as Alduin brings an end with a new creation follows, and the cycle of kalpa continues. Creation reversing is to resolve all the possibility of all kalpas, and Alduin is no ally to the Thalmor.
Can we say the player is mantling Akatosh or his champion by defeating Alduin? Or we can gather Shor and Akatosh into Talos who of course has bound Akatosh and Lorkhan together in the Wheel? Or in fact the player is acting as Champion of Talos?