In WoW, each class (with the Druid as an exception) gets three specializaitons, which are essentially their equivalent of subclass. "Specs," as they're referred to by most players, will also define your group role - whether that's Tank, Healer, or Damage (often referred to as DPS for damage-per-second). Every class has at last one damage spec, while only some classes can tank or heal. Usually, if a class can tank or heal, they only get one spec to do either of those roles, so, for example, every healing Monk is a Mistweaver.
Priests are the sole exception: they have two healing specs. The Holy spec is built around direct, conventional healing - just good healing spells that restore HP to their targets like you would expect, and a reasonable-enough analogue to the Life Domain.
Discipline is a bit different.
First, a caveat: I've been playing WoW for 20 years, in every expansion. I've probably healed in a number of dungeon runs I could count on both hands with fingers to spare. Healing in WoW is something I just don't have the sense for, and given that I'm very comfortable tanking (another in-demand role,) I haven't ever felt the pressure to play a healer. So, basically, healing is a part of the game that I have comparatively negligible experience with. But I do at least have a broad sense of the way that the various healing specs work thanks to being on the receiving end of them.
Over the years, Discipline has had sort of multiple mechanical identities as well as flavor identities, but the broad gist is this:
First off, WoW classes and often specs will tend to be much more narrowly focused on certain damage types, and while Holy's handful of damage spells (to let you solo in the game or contribute damage if the party isn't taking much damage) all do Holy (equivalent to Radiant) damage, and Shadow's damage spells do I think exclusively Shadow damage (which sort of amalgamates what in D&D would be Psychic and Necrotic damage,) Discipline mixes the two.
(As an aside: in WoW's early days, there were strictly 7 damage types - physical, fire, frost, arcane, nature, shadow, and holy. You could get gear that would increase your resistance to one of these types, which was necessary to make for certain raid bosses, though there was never any "holy resistance" and physical resistance was just armor. Around the second or third expansion, they got rid of resistance on gear. Similarly, they stopped having monsters resistant to any type of damage players could do. Even when fighting through the Firelands raid, a Fire Mage or Destruction Warlock, both of whom do a lot of Fire damage, will still work just fine despite fighting a bunch of fire elementals. Instead, damage type has become a kind of keyword for certain class talents to key into, like having a feature that temporarily boosts all Shadow damage done. At some point, they started introducing hybrid damage types, like Shadowfrost, combining Shadow and Frost, or Radiant, combining Holy and Fire, which would benefit from buffs to either but if something temporarily shut down that type of damage, like a spell interrupt, you'd be locked out of both types. I'm actually not sure if some of the newer damage types, like Cosmic, are hybrids or just brand-new ones (I could imagine Cosmic being, like, Shadow and Arcane maybe?) Anyway, damage type is a big part of the defining aesthetic of classes and specs.)
Next, from the earliest days, Discipline has had a theme of creating damage shields - the equivalent of Temporary Hit Points - as a major part of their strategy, preventing damage proactively rather than waiting for friends to take a big chunk of damage. But at some point, I want to say around when Legion launched in 2016, they got a pretty extensive revamp to incorporate a new central theme: Atonement, which allows you to heal your allies by damaging enemies. Discipline thus became the "damage to heal" spec (a similar theme used to be a major option for the Mistweaver Monk, though I believe that has been deemphasized, even if the Monk was doing this first).
The theming is very faint in WoW, but Discipline is vaguely flavored as kind of an Inquisitor-like figure, though this is barely hinted at in-game, and mostly revolves around its willingness to us both the Light and the Void.
So: how do we translate this into D&D?
Domain Spells:
1st: Guiding Bolt, Shield of Faith
2nd: Arcane Vigor, Magic Weapon
3rd: Prayer of Mending, Protection from Energy
4th: Guardian of Faith, Stoneskin
5th: Circle of Power, Destructive Wave
First off, Prayer of Mending is a new spell that basically heals an ally and then can jump to additional allies. I do wonder why we'd want Arcane Vigor as a Cleric, as it's kind of a crappy heal that's just there for classes that don't get any healing otherwise. But yeah, some decent stuff here, though the best stuff is already on the Cleric list.
Level 3:
Holy Bolt:
As a bonus action, you can use a Channel Divinity to make a ranged spell attack against a creature within 60 feet. On a hit, they take Radiant damage equal to 2d10+Wis, and you can choose a creature within 60 feet of yourself to regain 1d10+Wis HP.
This isn't great for the following reason: the healing only happens if you hit the target. So you can spend your Channel Divinity on something that might totally whiff. I'll also say that this could probably use some better built-in scaling, maybe having some fraction of your Cleric level added to at least the healing. It is a bonus action, which is nice (and something Clerics I don't think are always using) but it feels like, especially at higher levels, this will just not be worth using. (The healing is just slightly higher than a 1st level Healing Word.)
Atonement:
When you cast a level 1+ spell that restores HP to one or more creatures, each of those creatures gains a blessing that lasts until the end of your next turn. Whenever you cast a spell that deals damage using a spell slot, each blessed creature regains HP equal to the level of the spell you cast to deal damage.
This is a pretty direct translation of the WoW ability, more or less, though in that the healing is based on the damage you deal, as spell slots aren't a thing in WoW. That, though, is the rough part of this: at the very most, this could give 9 HP back.
And I think this is going to be an issue in general with how healing works in WoW versus how it works in D&D. In WoW, if you're in content that is of an appropriate challenge based on your level and gear, healers are going to be constantly casting healing spells on the party, constantly topping them up, and so a kind of constant "ambient" healing is really great. But in D&D, no Cleric is casting a healing spell on every turn in combat unless things are going really bad. That being said, things going really bad might be where this shines. If the party is fighting a dragon, for example, and takes a big breath weapon attack, you might cast Mass Cure Wounds, putting Atonement on the whole party. Then, the dragon recharges its breath on the next turn, and three of your party members all go down. Well, just shoot off a Guiding Bolt at the dragon and all those unconscious allies will pop back up with 1 HP.
Level 6:
Luminous Barrier:
As a bonus action, you can expend a Channel Divinity to place a magical ward on each creature blessed by your Atonement. The creatures gain Temp HP equal to your Cleric level plus your Wisdom modifier. While a creature has these Temp HP, they have resistance to all damage.
This is the reason to take this subclass.
So, we do need to have some big AoE heal, and sadly we cannot do Mass Healing Word on the same turn as this. I do believe that Holy Nova (a WoW spell) is being added to the book as well, which is basically a "heal my friends and harm my foes" emanation spell, which could work for this. But at this level, you're going to be giving your allies probably 10 Temp HP that, thanks to the resistances, is more like 20. It's not quite Twilight Domain territory, of course, and is more resource-intensive. But this is the feature that I think is going to make players really strongly consider this subclass. Just to check out the math, this eventually becomes 25 THP that kind of counts as 50 thanks to resistances.
Level 17:
Ultimate Penitence:
Holy Bolt gets more powerful in the following ways:
Ascending Step: When you use Holy Bolt, you can teleport to an unoccupied space you can see within 30 feet before you make an attack roll.
Ascending Volley: When you use Holy Bolt, you can expend a spell slot as part of the bonus action to hurl a number of additional bolts equal to the spell slot level expended. You can direct the bolts to hit one creature or several, making separate attacks for each bolt.
Why the hell would I want to use Holy Bolt anymore? I mean, ok, let's take this on its merits. This basically lets you get some scaling at the cost of a spell slot. If I burn, say, a 5th level slot, that's 5 bolts that each hit for 2d10+5 (presumably,) so like 16, and thus about 80 damage as a bonus action. Ok, that's actually not terrible, though we're expending both a pretty hefty spell slot and a Channel Divinity for it. And each bolt that hits is going to be doing about 10.5 healing.
I think the problem here is the resource cost. This only looks really good if we're expending a high-level spell slot that we could probably use more effectively with an actual spell. Holy Bolt doesn't have any inherent scaling, and given the massive power of Luminous Barrier, I really don't want to be wasting my Channel Divinity on it.
Overall Thoughts:
Boy, this would be a pretty bad subclass if Luminous Barrier weren't propping it up. But while Luminous Barrier is genuinely a very good feature (though only if we don't hold it to the same standard of the overpowered Tasha's domains) I think there are enough other good Clerics that I don't think I'd recommend this one.
Again, I think one of the central problems (and this is a bit of a theme in this book) is that WoW and D&D, while thematically similar, are ultimately very different games, and strategies that are amazing in WoW (like constant streams of small heals on everyone in the party) are not nearly as effective in D&D. In a similar manner, damage-over-time effects are a huge part of how WoW plays, because you can be fighting even a minor monster out in the world for around 30 real-world seconds, meaning that DOT could tick like 15-30 times, whereas in D&D, combat rarely lasts more than 4 rounds, so ticking damage is only going to have a few opportunities to do anything. In the interest of re-creating the feeling of WoW gameplay, I think some of the design here suffers from being poorly optimized to work in D&D.