Gonna have to be more precise. You mean the healing kit?
While it's bland as vanilla ice cream dipped in milk, each of its abilities has a use case. Many of them are close together, though.
Right, this is generally good design. Since it was a DPS gain, it wasn't "a decidedly AOE skill". It was a "single-target rotation skill also useful in AOE", which is a much better game design than having a host of single-target buttons and a host of AOE buttons that don't interact and don't stray outside of their use-case.
That's like saying Fleche and Contre Sixte should share a CD and you use one for single-target and one for AOE (like WAR's two oGCDs) instead of just having both be used in both single-target and AOE rotations.
Though...I'm not entirely sure if you're arguing this is good or bad. Depending on how I read your post, I could see either way, though I think we may be in agreement on this point? I also agree that Flare is the iconic BLM ultimate spell (like Holy is for WHM); go figure they're both relegated to AOE only uses. Especially since a number of versions of FF games, Holy (and maybe Flare...) are single-target abilities...
This. This was kidna my point about "Vanilla WoW".
FFXIV just doesn't have enough add/cleave/multi-boss fights for this to matter. There just aren't cases where you're actively swapping between single-target and AOE to make the two rotations being distinct have a point. Even when we get adds in fights, it's usually a short DPS check mini-phase that's one-and-done, not something recurring or that you're shifting into and out of AOE and single-target. Like imagine a fight where every 60 sec or so you'd have several adds spawn. Not only would this give the OT something to do, it'd give people a reason to have AOE skills on their bars, and give some Jobs like MNK (which can swap into its AOE rotation on the fly because of the way its stances work) a smooth transition to slide into AOE and then back to single-target.
But we don't have that, making AOE buttons largely "we have single-target rotation at home".
I think this largely depends on the player. ASTs will tell you they're the punching bag right now. SCHs might, too. The only Healer Job right now that won't say they're the punching bag are probably SGEs, and that's just because they're new to this expansion and probably A BIT overpowered.
I think the best solution is to have heals be damage neutral and DPS be semi-free. What I mean by this is, systems like WHM's Lilies reward actually healing. IDEALLY, it wouldn't be boosted by party buffs so using it or Glare wouldn't matter (that is, it's not TRULY damage neutral because party buffing a Misery gives you 4x the benefit of party buffing a Glare right now), but it's close enough people not doing it aren't doing a completely different universe of DPS by comparison. But if healing was DPS neutral, it would mean you could swap seamlessly to healing and back to damage.
Healing being gated behind DPS is a bad design. For example, imagine a Healer Job where we had, say, SGE, and it had no healing GCDs, and only Addersgall spenders as oGCDs, and it gained an Addersgall every third Dosis cast or something. This would be bad because there might be times you need to heal, but you can't until you DPS a few more times. (Note that this is distinct from "damage spells do healing"; current SGE does do healing by casting Dosis, but it has both oGCD and GCD heals to augment that with or fall back on.)
Conversely, having damage increases locked behind doing healing is bad design, as you hit on, because when you don't need to heal, you basically are having to overheal to do optimal DPS. While this is TECHNICALLY true with WHM, the Lily system is flexible enough that you should always be able to do some useful healing with it (casting Solace on the MT, for instance), and the damage difference of using it optimally or not is fairly narrow.
But even with these constraints, there's a lot that can be done. For a simple example (not suggesting this, just by way of illustration), imagine SGE had a 1-2-3 rotation like MCH, where each hit did more damage (like MCH), and the amount healed to the Kardia target was equal to that potency. This would mean using your 1-2-3 instead of 1-1-1 increases your healing as well as your damage...but this is Kardia healing, so you still have your GCDs, oGCDs, and oGCD AG spenders to heal with even if you're constantly flubbing your "rotation". Such a system isn't locking away healing or damage behind doing your rotation correctly, while still rewarding proper rotation use since your healing burden would be slightly less.
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I will also note - because people seem to say this a lot - "breaking your rotation to cast healing spells" is no longer a thing. Look at PLD. Press 1-2 then press Clemency than press - 3. Did you see what happened? Your combo didn't break due to you casting a healing spell. I think they changed this with 6.0 with a lot of the "doesn't break combo anymore" things (like Shield Lob doesn't), but spellcasts no longer break combos unless they're combos themselves. Combos break other combos (Weaponskills), and caster combos (PLD swords and RDM Resolution combo and NIN Raiju) will break/be cancelled if other actions are used, though this seems to be due to the "X ready" buffs falling away if other actions are used. Something not strictly necessary either - Verstone/fire Ready don't fall off like that - but it's just the way the more hard "combo" magic chains seem to work. You also see this with stuff like GNB Gnashing Fang not being broken by the use of Double Down or Sonic Break, only by the 1-2-3 or 1-2 (AOE) combos. BUT, note that the Continuation (again an "X Ready") buff WILL fall off, losing you a Continuation attack, if you hit DD or SB.
I don't think they've coded "spell combos" into the game yet. There are Weaponskill combos and then there are "X ready" effects.
Though this does seem to be based on their whim. For example, RDM's 1-2-cast spell breaks the -3, doesn't matter if Enchanted or not. Likewise, Jolt-1 breaks Dualcast. And using any melee strike or spell that isn't Holy/Flare->Scorch->Resolution breaks that chain. Dualcast is probably a "X Ready" effect by a different name, while the Resolution combo seems to be more similar to Confetior, though I think both of those are "X Ready under-the-hood" where they don't give you an "X Ready" buff outright, but function the same way and are likely coded the same way.
...but then you have "Verstone/fire Ready", so...I dunno, it's kinda whatever they want to do. But point is, it absolutely COULD be done for a Healer Job to have a combo system that doesn't break for spellcasts.