Astrologian buffs confirmed

[Kietsu]

Compare that to Selene's buff: 3% damage AND healing speed increase, divided by 2 since it's only every 30 seconds = 1.5%, times 8 as it hits the whole party = 12% DPS AND healing increase.

This right here makes absolutely no sense. Selene doesn't increase your party's DPS output by 12%, she increases it by 1.5%.
Still, you got me thinking!

A comparison of Fey Wind to the Balance is a bit tricky, because damage != attack speed. But let's give it a whirl.

If you somehow manage to play an Expanded Balance or Arrow every minute (and let's be clear here, that's not going to happen), you're giving the whole party 5% more damage with 25% uptime, meaning you're bolstering your party's DPS by 1.25% - this is outright less than Fey Wind. An Expanded Balance combined with Celestial Opposition increases the party's DPS by 1.5% for the one minute span of time before the next Expanded Balance, but this can only be done on every third Expanded Balance. Because the Arrow doesn't boost the damage of oGCDs and similar things, it's a bit worse - but Selene has the same problem. Still, Selene is 100% reliable.

However, there's a scenario where Astrologian's buffs should really shine: Burn phases. In burn phases shorter than 15 seconds, the uptime doesn't matter - only the potency does. To make matters better, we can actually set up for this semi-reliably, though doing it too far in advance means we just stop drawing cards until the burn phase.
In this case, the Astrologian buffs the party's DPS by 5%, while Selene only manages 3%. (And again, the Arrow and Selene actually perform a bit worse than this)

tl;dr cards suck for buffing raidwide DPS except during burn phases.

(I tried figuring out if it's better to aim for single target buffs over AoE buffs but because all of the RNG it's insanely complex. Short answer: It's a good choice in 4-man but falls flat in 8-man because each individual DPS player has a smaller chunk of the overall impact)