I just cant grasp this part of the main quest. Suppose your player is a khajiit or bosmer, you visit alduin in soverngarde, and enter the hall of valor.

But what Tsun says after you defeat alduin is the most confusing part. He says that when the time is right, you can join others in the hall of valor. But khajiits or redguards shouldnt belong to sovergarde in the first place!

Did the developers mess up as usual?

Sovengarde is in essence an Aedric realm, not unlike the various Daedric realms.
Which one of the many one will land in will ultimately depend on one's beliefs in action.

Kodlak's Cure Quest is an example of this.
Setting him free from the werewolf curse allows him to enter Sovengarde, if done before you reach this part of the main quest.

I think that they make an exception because your character is Dragonborn.
And you have in effect saved Sovngarde as Alduin was consuming the souls that dwelt there.

You 'just cant grasp' it? http://www.markhorne.com/images/scrollquill1.jpg, rewrite the story.