This has been re-hashed over and over. The terms are that if they want to discount steam provided keys on another platform they have to match that price on Steam. Steam keys are free to generate for them. They are free to distribute them on any platform. But the deal they make when they generate the steam keys is that they will adhere to the pricing rule.

If they want to discount keys generated on Epic’s store, then they can generate and sell them at any price they want.