Yeah, the Elder Gods stripped him of his amulet, where a lot of his power came from (it was also a Kamidogu). That's what the whole hubbub surrounding the Elder Sub-Zero and Mythologies was about; if Sub-Zero were to get Shinnok's amulet back for Quan Chi, he'd be at full power and he could escape from the Netherrealm.
Tanya is not a cliche "evil girl" character. That would mean she merely be a lady henchmen of a powerful, evil figure, which isn't true; she is more than that. She wasn't even revealed to be evil until her MK4 ending, where she led Liu Kang into a trap and ultimately his death at the hands of Shinnok. She doesn't just betray good people, she betrays evil people, too. Have you seen her Deception ending? There are no "cliche bad girls" in MK, and yes, I'm counting Kira.
