I mean, it would basically make enemy-casted Bole the best card in the game instead of AOE Balance, unless the modifiers were changed. A better Trick Attack than actual Trick Attack, that also stacks WITH Trick Attack as well as things like Chain Strategem? So you might be saying, "okay, make it 5% damage taken increase" but that's still missing the fact that you can have it up every 30 seconds whereas AOE Balance can only be up every 60 seconds (barring Sleeve Draw). So THEN you might say, "make it 2.5% damage taken increase then" but then that's still a pretty huge buff to AST's kit overall since that essentially removes a "dead" card from your kit, meaning that AST actually has zero "dead" draws now (barring back-to-back Spire/Ewer).
I still maintain that removing the RNG is the way to go for AST. I WANT to be able to use my defensive card once in a while without wistfully thinking "I should have Shuffled this into a DPS increase". I don't want my defensive/support cards to turn into offense cards, I want to be able to use them without feeling like I'm giving up something better in return. Minor Arcana was a mistake that only enforces the idea that there are "bad draws you should get rid of", Spear change was a big buff but I would have rather its original function received improvement (reduce CD timers on moves that are already on CD, wasn't hard to fix tbh) rather than changing it to just another damage buff. It's too late to go back to that now, but I'd much rather the cards be on-demand use with cooldowns relative to their strength, so that you can't just sack Bole/Spire/Ewer in the hopes of MOAR DEEPS INCREASES. It's binary and dull. Also, removing the RNG element opens the door for the devs to give us new cards in the future without making the players feel like its another wrench designed to dilute Balance/Arrow/Spear RNG.