Quote from Sikor
That's totally true but he wasn't possessed right after "stoning" his head... He was losing humanity partially. And yeah, soulstone definitely had some kind of influence on Leah but she's still Aidans daughter.
This is Blizzard. They looooooooove the dark woman concept. Leah is totally gonna be Diablo's daughter. A bit of corruption around the edges is boring and too subtle for this series.