I am playing in Legendary. The quantity of mutagens we can get with prisoners is an abuse and allow full upgraded mutoids in early/mid game when your soldiers are far away of it.
But to be even easy and worst, the base attacks are to weak and an offer of mutagens. With the right team waiting for them, is easy to imprison ALL the pandora attackers and get 1000+ mutagens in a single base defence, what allow build a full upgraded mutoid.
Link to vote in canny feedback: Offer of Mutagens in Base Attacks | Voters | Phoenix Point