Ok, try to follow my train of thought:
In D2, D and M's soulstone gets destroyed. In D2X, B get's destroyed.
So are they banished back in Hell or do their spirits float aimlessly in Sanctuary still?
Cause they have to be in Santuary in order for Adria to gather them right?
But hold up. How is Adria gathering them? With the Black Soulstone!
Wait what, but the Black soulstone isn't finished being built yet (which is a quest in D3 where you finish building it)
So how did 5 Lord of Hell's souls gets into the Black soulstone that was never completed in the first place?
And, assuming Adria had a working black soulstone (what), why the heck does she not have it when we find her and why the heck do we need to (re)build it again in Act 3?
THIS GAME MAKES NO SENSE.