I feel like there should still be unique effects on each of the cards. Like, keep the overall damage increase for all the cards, but also include a bonus depend on the card you used.

Balance: 5% Direct Hit Chance Buff
Spear: 5% Critical Chance Buff
Arrow: 5% Recast Time Reduction
Bole: 5% Damage Reduction
Ewer: Increased MP Regen
Spire: Increase HP Regen

Hell, maybe make it so that Divination requires a card to be drawn to use and that bonus effect is spread to the entire party.
Will people fish for the best card still? Yeah, probably, but the best effect is still on the card, the flat damage increase, so it's fine either way.