The intended price for a quest potion is supposedly 1 dollar each. When buying thru credits, we are not actually saving, we are just paying the exact amount that we should pay for every quest potion. But why isn't it worth it to buy quest potion using DEC? Well, DEC's price was originally 1000 DEC for 1 dollar. But, because of the SPS airdrop being implemented for 1 whole year, and people get more airdrop rewards according to the amount of DEC they have in-game, people are hoarding DEC in-game. And this affects the DEC value by a ton.
Here's why... The price of DEC is dependent on the amount of DEC distributed to all players, and if more and more people are hoarding DEC instead burning them, the price of DEC will surely appreciate.
This conclude to the following: