So is Alduin supposed to take damage when you use Dragonrend to send him to the ground? Because if so, my game is broken. I use Dragonrend and he lands but takes absolutely no damage. Any ideas on how to fix?

Reading the description for Dragonrend I don't think he is supposed to take damage it is only used to make him land.

I fixed it. He wasn't taking damage from swords or spells when he landed was the issue. However, I discovered that I could fast travel away from the battle at my last save then travel back and it was fixed. Weird.