Board Thread:General Discussion/@comment-13436964-20130726221035/@comment-10781165-20130730035022

Miraak has a shout to instantly kill a dragon, making dragonrend a little redundant. I doubt it would work on Alduin but it may have damaged him. Also, I feel like under his servitude to Hermaous Mora, he learned a plethora of shouts, Dragonrend included.

Lastly, Miraak comments saying he could have defeated Alduin way back when he roamed Nirn if the Dragonborn has already slain Alduin before he first encounters Miraak. He's arrogant and cocky with good reason to be, he's extremely powerful.