So, these things can actually work completely the opposite to what you might imagine, depending on how the design is made. As an example, movement. If you have to move, as a WHM now, you have to sac 310 potency per GCD, because you cannot cast Glare while moving. Maybe you get lucky on some, and have a spare lily to burn on overhealing to stay damage neutral, Dia needs refreshing at that moment, you can blow Misery there if it's ready, or you can swiftcast if you really have to. But, there are some instances where you're just gonna have to suck up the damage loss. However, if the rotation was changed to how I'd personally like to see it, that is, Dia shortened to 12s (potency rebalanced to compensate) and a new 15s instantcast GCD added, then the issue of 'mobility' is actually easier to solve, not harder. You are more likely to have to refresh Dia at that point, because it's got a shorter duration, and the new move might be up. Even if it's not up, you could hold it to use it for mobility, at a damage loss in the moment yes, but as a damage gain because you filled a GCD that would otherwise be empty.
On which note, leading onto the other point: Damage gains of 'full rotation' do not need to be miles ahead of the current spells, contrary to what SE would have you believe with their Communios and their Double Downs. As an example again, I could (and did) suggest that the 15s CD's potency be 350, where Glare is currently 310, or probably 320 next expansion. So, ignoring that new spell completely, for an entire minute, would lose you 4 uses, a total of 160p (or 120 next expansion). About half a Glare per minute, or less. Optimizers don't always optimize because it's a massive gap in damage (see: Energy Drain), they do it because it's just simply 'more damage'. It could be a gain of 50 potency a minute instead of 160 and they'd do it. As long as potencies are balanced well enough, and the DPS check is balanced around 'the current kit' and not 'the extra 5-10% you can eke out by optimizing', then the 'enrage issue' isn't an issue. As long as the player uses something in that GCD, it wouldn't matter what, from a 'trying to clear the content' perspective. 'Doing it right' would just grant a little bit of leeway, not make-or-break the enrage check (ideally)
Also you're right on 'gauge that is filled through executing DPS rotation' to an extent, however A: the gauge I suggested is for a healing skill that is damage neutral (like how Lilies pay for themselves via Misery's refund), and is damage positive only by spending the refund skills in buffs ala Misery (since the refund is tied to casting Glare/Dia/the other one, this would mean using the gauge at X:58, else you'd have to AFK til the buffs go out), and B: I rewrote it to also include non Lily heals, such that if there's a hard HPS check (Harrowing Hell for example), the player can still build gauge, because it seemed silly to be locked out of building towards a healing tool because you were too busy healing. I wouldn't want to have a gauge spent entirely on 'damage positive skills' on a healer. Rather, I think the way to do it would be what I went for, a gauge that gives access to more healing or mitigation tools, that, if used well, can increase the player's DPS indirectly by removing more 'damage-loss GCD heals' like Medica 2. Well, at least for WHM
Pneuma's tagged as a spell (and therefore on the GCD) so it can benefit from Zoe, and probably also cos the devs wanted to give it a cast time so it could have a cool animation. IDK what Macro's deal is, but I sure would appreciate it if it were able to put up shields via Neutral Sect, if it's gonna remain on the GCD (that might be too op though)