Yeah, which is why SE backed themselves into a corner with an incredibly hard to tune class. They undertuned both its healing and its buffing because they were afraid of replacing WHM or SCH entirely and now it's not even good for farm content because it can't reliably make a clear easier via DPS buffing.
This is further worsened by the fact that they flattened the differences between healers by giving WHM more oGCD heals and MP Management options and SCH more burst heals and AoE heal options while lowering the fairy's contribution. The differences between SCH and WHM in terms of healing are marginal and SCH just has an edge in accuracy-less DPS.
And then they threw AST into the mix who can be a worse version of either healer without any of the oGCD skills and worse potencies on every measure and inconsistent marginal buffs.
Giving them more healing output is actually the safer option since their card buffs are generally weak and unreliable. If they had similar healing outputs to the other healers without access to the oGCD abilities they would be able to complete content more easily without totally replacing WHM/SCH since they are still required for progression content due to safety nets and DPS ability, while you could bring an AST to get the sameish healing but a smidge of a chance at meaningful DPS increases through cards (though the cards are way too unreliable right now to bring an AST solely for those).
If they buffed cards, AST is either still not as good as healing to make those who are hungry for world-first bring AST and therefore relegated to 4th tier clears/farm content, or their buffs are powerful enough that they can replace SCH as a DPS increase and leave the bulk of healing to the WHM OR even worse IMO, they replace WHM entirely because SCH + AST DPS is greater than any benefit WHM can provide.
The main problem is that, because of RR AoE, any DPS buff you can give out as an AST is extremely multiplicative with gear scaling vs. AST being able to DPS on their own vs. SCH both being able to DPS on their own AND getting to buff DPS via Selene (however slight it is). AST cards + AST DPS have to exceed SCH DPS + Selene raid DPS if they don't change AST's healing potencies. They currently don't due to unreliability of the buffs and weak MP management meaning they can't actually use their DPS skills most of the time.
It's a very fine line to walk which is why they are taking so long to buff AST after the minor changes in the hotfixes.