This is honestly where I thought the story was going in 9.2. It at least would of rationalized why Zovaal and Sylvanas wanted to destroy it.
I think the truth (or at least a version of it) is hidden in the updated cosmic forces chart. Life overlaps with the Void and Disorder. So perhaps life in the WarCraft universe is unnatural and chaotic. The Shadowlands might have been created to keep order of all those moral souls that perish. Maybe otherwise they would overwhelm the forces.
But the chart also features two serpents devouring one another. One dead and one alive. So its connection must go both ways. Maybe those souls obliterated and turned into anima are necessary for new souls to exist. Maybe souls like Kel'thuzard and Garrosh are gone but will get reincarnated into new souls.