Sithis as the Deity of Death in Form of Separation

There has been talk lately of ESO's portrayal of Sithis as a grim-reaper style killer in Argonia, where we see a snake-like Aspect of Sithis. Most people don't like this because it paints Sithis as a generic death deity when we already have Arkay as the god of life and death.

However, I do not think Sithis as a Death Deity is entirely dead in the water.

Speaking strictly from a Doyalist standpoint, Arkay doesn't have to be the only god of death. He represents death as a cycle necessary for natural existence. He's idealized and looked up to by mortals because it makes it seem like death won't be such a bad thing after all.

Sithis, on the other hand, can be represented as a fear of death. He's the death that separates us from loved ones and comes suddenly in the night in an untimely manner. This makes sense, considering how the Dark Brotherhood worships him.

It also fits with what we already know of Sithis. He's division and misanthropy. He would revel in killing because it separates. He hates everything that is, and wants it to be IS NOT. He wants to "murder the world".

He can't, because he is being held in check by Anuiel. But he occasionally gets his fix by messing around in the Aurbis, such as when he sent Lorkhan to the et'Ada.

Any aspect of Sithis mortals have run into on Nirn isn't the primordial being of Sithis himself. It's a piece of himself he has lowered enough to communicate with lesser creatures.

In conclusion, I think there is no reason why Sithis can't serve the role of a Grim Reaper-style being like the Dark Brotherhood believes, but at the same time more than that. I think it would serve as a fine addition to the Aurbis.