I feel like the finite soul thing simply contrives conflict in what I believe is an uninteresting way. The demon god and undeath god no longer become enemies or allies based on ideological grounds, but we will need to fight them because they are hogging a finite resource.

There isn't really any interesting outcome to a soul-shortage. It seems like it really just come down to having the artitect give us more souls, or bully demon boy or undeath god to shake some souls loose.

Edit : Further thoughts, My problem is that it seems like every other god has no reason to care about souls except at a seemingly random point when it suddenly an issue we need to worry about, and it will effectively force all humanity-sided characters to side with Kath since there isn't really any alternatives.