Add Alchemy as a separate thing
Add Alchemy as a separate gamemode entirely, and let historic become the eternal format for MTGA.
Take the opportunity to move the digital only cards out of historic and into historic alchemy instead.
There is only two reasons for why you wouldn't do this; Either you intentionally do this because you believe you can get more money, or you simply haven't understood why an eternal format is needed.
I'm choosing to believe the latter for now. Revert this absolute travesty of a decision, and everyone will be happy, or keep your current course and at least I will no longer spend any money on your game.

-
Problem Solved#33478 commented
Many players do not enjoy having to play against Alchemy cards in formats like historic and historic brawl. There are many reasons why we dislike these cards so much. You can keep Alchemy as its own separate format but please stop allowing these cards to pollute existing formats. I'm begging you.
-
wildarms420#86733 commented
Alchemy should have been a separate game from Arena. It feels as if the game was forced into bad decision making. I can't come back and play it just isn't the same game I was looking for 😔
-
LEGOFett#11638 commented
I am uninstalling all all platforms until the following two decisions are undone: Not refunding wildcards for nerfed Alchemy cards (a practice Hearthstone has done for years), and not having Alchemy nerfs effect Historic. You lost another paying customer over greed and mismanagement, WOTC. I am not willing to play Historic with these decision in place. I play Historic because it is a Non-Rotating format. Spending wildcards is no longer safe in Historic because of these decisions. You are making cards we spent wildcards on unplayable in Historic due to setting them to an appropriate power level for Alchemy i.e. Standard (not Historic) with not compensation for sunk cos