The DEC cost for Quest Potions should've been updated at the same time that you removed the Credits option. As it is, no one's going to spend that amount of DEC for Quest Potions.
Doing it as it is now indicates that the devs are really trying to plug a hole without fixing it in the first place.
Telling us that there are new Rewards don't mean much if new players get less opportunities to get cards anyways. Not everyone has a bag full of DEC waiting to be spent on Quest Potions, especially in Bronze/Silver.