I'd swap Balance and Spire effect.
Because Solar seal is purely support cards while Cestial is purely damage.

This way, for each seal, you have an additionnal support effect if needeed, and if not, you can just go for slighty better damage increase.


But there's a slight problem with that system. You can't use a card without messing your current loaded seal.
If we had to way to save seal so that any other cards used won't interfere with it, it could work.

15% damage for minor arcana cards is a bit too much.

Otherwise, I had almost the same idea as you, so i'd support reworking the card system in that way.
Same for Divination. Having multiple effect would justify this awfully long CD.