Divination also stacks with the cards. So while it is 6% on the entire group, there is also a high chance that you'll be using it in conjunction with around 2 or 3 6% or 8% buffs. Which is usually the case, as you should have 3 card buffs rolling alongside the first divination.

Not to mention if you keep on top of your seals, your subsequent Sleeve Draw can be used to pump out 3 minor Arcana buffs on cooldown. Which are 3 8% damage buffs on 3 of your dps.

So best case scenario, on your opener you'll have one 8% buff (a prepull minor Arcana) 3 6% damage buffs on 3 dps, and 6% damage on the group.

Then at 2 mins you'll have another 6% damage plus one 6-8% damage due to draw lining up.
At 3 mins you'll have 3 8% buffs,

At 4 it will be the same as 2 min,

And then at 6 min you'll have Divination + Sleeve up, meaning 6% damage on the group + 8% damage on 3 of you dps, plus another potential 6% or 8% on the 4th dps depending on draw cooldown.

And the whole time you'll have a card drawn every 30 seconds, which is a potential for 3% at worst, and 8% damage at best.