*blush*
I've been thinking about skills like this a lot of late within the domain of active mitigation. Since Legion, though, my favorite example has actually been closer to the Warrior's oGCD toolkit, however (especially back when Focused Rage was still available). Take their Ignore Pain, for instance. To me the ideal design concept for active mitigation should have both choices (not necessarily between other defensives) and application variance. Ignore Pain's interaction with its alternative general resource (Rage) spender, the nuke-buffing Focused Rage, gave both—with or without the (obligatory) Vengeance talent (which traded out choice play for pace play, but also allowed the player to save more rage on one choice than the other through refocusing their priorities while still trying to meet incoming and outgoing windows of play). As effortless as that key was to hit, its timing meant something. It wasn't just a buff you maintain (which is what Holy Shield typically felt like to me).
I'd like to somewhat avoid concrete examples for now, especially within the combat system as it is now, largely just because I imagine these were meant to illustrative spit-balls, and any counter-suggestions I'd give would be just the same. And because—broken record here—I feel like certain parts of my suggestions will never quite click without some larger underlying revisions to combat (stagger, interception, revisions to RNG mitigation, certain new mitigation mechanics, certain new damage splitting mechanics, etc). For now I'll just leave it at this.Just a side-note though, even maintenance buffs like Holy Shield can make that somewhat engaging, especially if they're not oGCDs. Now, that will sound debilitating to some, especially anyone not assuming that the class is (gasp) balanced around that very fact, and is not therefore held back by it. By it being on the GCD, it now has judgment—it needs to be weighed against other choices. Is it about to run out, making some space between this and the next GCD potentially far more painful? How much would be wasted if one were to replace it right now? Depending on how those stats are tracked by which the decision, and how the shield mechanically lasts (by damage or hit count, etc.), it can be either involved or just bothersome. I feel like that's something any MMO ought remember a bit better in regards to some abilities before their initial implementation, rather than having to patch them out later or pretend they're not held back by those small but highly gameplay-affecting details. Some minutia really matter.
My entirely personal preferences lies with adding as few class or ability-specific gimmicks as possible, while still making them as involved as possible. For instance, even if a stance does something as simple as adding 15% damage, that should be felt through certain benchmarks shifting in the interactions between the attacker and the attacked just because of that damage bonus itself. Even what is simple should be capable of feeling highly involved. Where it does not, that's not a requirement to give the tooltip and extra paragraph's worth of effects—it just means there aren't enough facets of interaction in the first place, universally speaking (or because of some line-up in that interaction). And those are broad mechanics more so than anything unit- or interaction-specific (which would simply be where those marks occur and how the decisions they bring out). Take any actual fighting game for instance, especially where one of the guys has a "Minus Strike" of sorts (like Shugoki's Charge of the Oni in For Honor). It's no longer then just chunking or chipping away at enemy health. Health matters. And so timing matters. Early burst can leave you dead. And yet it's still just health, and one stupidly simple modifier to make it important. That's what I'm looking for in the changes I might recommend. As a tank (or anyone, really) I want things to look forward to beyond just my CD refreshing (something a bit more on the additive side), rather than just thinking about how long I can hold out with my buffs going on CD and their buffs dropping off two by two or so (a more... deductive model, if you will). I want to feel like I'm really "in the fray." We have now slightly through Low Blow and Blood Price, etc. But I want more... a lot more.
One of the things I've suggested to that end before was a revised TP model. That'd be a ridiculously large change, I know, but hear me out for illustrative purposes. By returning TP to a primarily generative resource, building from damage, mitigation, healing and healing dealt and perhaps even damage taken, to differing degrees between different jobs or even stances, there would naturally be an improved output when "in the fray", especially for tanks. Allow TP to then take an effect on or be spent on combo-rushing, thematic tools, extra oGCDs, cleave mechanics, empowering spells, etc., and—in this case the most important bit—defensive abilities, and you have naturally have choices asked of you. Do you accelerate your combos in order to open into your mitigating weaponskills quickly, burn down an enemy (either to undamaging, dead state or stagger him for the time being so he can't do shit to you or anyone else), build defenses, pop utilities... what? Everything has some visible benefit, but you're aiming for the mix that would most produce the outcome you need.