Why don't astro cards stack?

[HyoMinPark]

As for actual suggestions...
They shouldn't stack if they are the same card in my opinion.
If they are different AND from another player, I don't see the harm. I think the RNG element is enough to not make this too overpowered, most of the time anyway.

Stacking an AOE Balance and an AOE Spear in an opener would not be as broken as two Balances stacked, but it would still be overpowered. This would not serve to balance the healers, but tilt scales in the favor of AST even more than it is now (especially when you compare them to WHM, which is the healer AST “competes” against).

They'll have to do something with the cards for Shadowbringers anyway, due to removal of TP and therefore making the current Spire redundant. Someone suggested on another thread this could become a direct hit buff which I guess is the last remaining stat to receive attention thus far.

Spire will either be reworked into another type of buff or deleted entirely. That they have to change Spire doesn’t mean that they should allow for AST buffs to stack—especially since no other jobs can stack their respective buffs. Again, this would not help the healer balance they are wanting to do going forward.

Also, do savage/ultimate/extreme organised parties typically NOT have 2 players of the same class and therefore this isn't a problem for them anyway?

During Creator when AST Balance was +20% for single target and +10% for AOE, it was not unheard of to find speedkills and parse groups running double AST. It’s fallen out of favor now since Balance is not as strong as it used to be (and with good reason). That said, optimized groups already oust one healer—allowing stacking buffs has the potential to oust two.

Double jobs only impact the ability to build LB. LB building isn’t that critical for most fights, and it didn’t hold people back then so I don’t imagine that it would hold them back going forward.