Question: It's been shown that Zankou has the ability to steal powers through touch utilizing Power Absorption. Yet, why did he need a potion to steal The Charmed Ones' powers?
Answer: He can't steal powers from good witches because he is evil.
Answer: Zankou needs to kill the demon or witch to steal their powers.
Show Ghouls - S7-E15
Question: If they already vanquished Sargon in "Soul Survivor" and burned all the contracts, shouldn't the deal between him and Count Roget have been broken too?
Answer: No. Because it was in a time loop that only him and the Count knew, and as such even though in the present Sargon was vanquished the time of the time loop he was still alive.
Answer: Yes.
Chosen answer: Zankou can only steal the powers of demons - he cannot steal the powers of good witches because he is evil. He would need a power stripping potion to do that. Now that he has control over the book of shadows he is now able to make the power stripping potion.
Stephen Edmonds 1