I have not fully level up my AST yet, so I could only give you some explanation on new Card system
so new card are boost DPS, depend on the nature of the card, it either have bonus melee DPS and tank or it give bonus to range DPS and healer.
The basic buff is 3%, and 6% if given to right class or self.
There is a easy way to see if the card bonus is melee/tank or range/healer

melee/tank card will have blue outline



range/healer card will have a purple outline



Each card you use will give you a seal, total 3 seals can be stack up and there are 3 different type of seals. What type of seal can be see on the card
on top of the card you will see either a sun, or eclipse moon and the universe? (cant really tell what is that representing celestial)
you can only hold 3 seals max at a time, new seals will replace the oldest one.
Lining up 3 different seal will give the max buff for Divination, a AOE buff, the dmg buff is 4,5,6% depending how many different type of seals there are

when your Divination in CD and seals line up. Card can be use for Minor Arcana
this will turn your card into either lord of Crowns or lady of Crowns, give dps buff and have melee or range bonus like the normal card but they dont give seals. However, they give higher buff, 4% and 8% instead of 3% and 6%