Honestly the reason why Purify is 2 mana is that they didn't want to print the effect at 1 mana, just because Gadgetzan Auctioneer exists. I love Gadgetzan Auctioneer in Miracle Rogue, but it really should just be a Rogue card, so the other classes can be allowed to have some good spells. Having a low-cost spell in your deck should be at some cost to you in the form of consistency and card advantage, and these low-cost spells are designed around this (1 mana deal 2 damage is reasonable, but 5 mana deal 10 damage would be oppressive). But when a card like Gadgetzan exists, suddenly all of the low mana-cost spells which seem so balanced on their own lose 100% of their downside and just become super overpowered.
That being said, it's not the weak cards that define a set, it's the strong ones. Purify doesn't make Priest worse, except in arena.
That being said, it's not the weak cards that define a set, it's the strong ones. Purify doesn't make Priest worse, except in arena.