Suggestion: WHM change

[Katoar]

GCD-s can have higher than 2.5 seconds recast time
WHM already has Presence of Mind
WHM has no DPS kit just random buttons for every occasion and one DPS refund button

You are jumping to conclusions. No potency has been set for Drought or Seraph Strike. It is all a matter of balance to make Tree of Life a viable choice but if we want to make it useless (talking about removing HoT) it is going to be useless. The Tree of Life's purpose is to enable White Mage to use all five stacks of Blissful Sacrifice every 30sec while under its aura. This is far more valuable. While we are at this I will move the removal of max HP cost from Blood Spilled to one of the benefits the Tree provides.
Also, Using Seraph Strike for DPS gain instead of going for Earthquake to cast Spiritual Ray will be pointless and will result in DPS loss.

So every 30 seconds you could use Tornado. After 60 more seconds you could use Flood for Seraph Strike, leaving you at 4 stacks. With your next Sacrifice you'd be at 6, which means you can either do another Tornado/Flood or just one Earthquake during the raid window.

I am uncertain that you have fully grasped what I have written.

The moment the detrimental effects of Blissful Sacrificed are removed, all thinking required evaporates.
As mentioned in the OP, Enduring Faith stacks are lost when Blissful Sacrifice expires or is cleansed through Exaltation.

Drought is meant to be an offensive maintainable buff.
The Tree of Life is meant to be a supportive maintainable buff
Seraph Strike is meant to ease the obtainment of the Tree of Life buff as with no stacks of Blood Spilled it will cost 60% hp and 30% of max HP reduction for a short time.
Spiritual Ray is meant to be a rewarding DPS spell for figuring out how to survive despite using five stacks of Blissful Sacrifice.
Lastly, I decided to use HP instead of MP as we already have an oGCD that synergies well with self-detrimental status buffs - Lilybell. And we can hopefully look forward to the implementation of more oGCDs like it.

[SirShady]

GCD-s can have higher than 2.5 seconds recast time
WHM already has Presence of Mind

Yes, but almost every GCD is on a 2.5 recast time for a reason. Making one of White Mages GCD's take longer serves no purpose and doesn't fit its identity. You CAN do it, but why? Does it just deal that much damage?
You would never hold onto Presence of Mind just to speed up one GCD if it didn't align with Spiritual Ray. That's a DPS loss.

You are jumping to conclusions. No potency has been set for Drought or Seraph Strike. It is all a matter of balance to make Tree of Life a viable choice but if we want to make it useless (talking about removing HoT) it is going to be useless. The Tree of Life's purpose is to enable White Mage to use all five stacks of Blissful Sacrifice every 30sec while under its aura. This is far more valuable. While we are at this I will move the removal of max HP cost from Blood Spilled to one of the benefits the Tree provides.
Also, Using Seraph Strike instead of going for Earthquake to cast Spiritual Ray will be pointless.

Why would I ever hold onto all these stacks to use a heal over time when I have a superfluous amount of heals in my kit already and can instead go for Spiritual Ray or Seraph Strike? Why would I ever go for Seraph Strike if building up to Spiritual Ray does more overall potency?

I am uncertain that you have fully grasped what I have written.

This we can agree on. From what I'm seeing, it doesn't make a whole lot of sense. Surely you'd just use all your stacks for Spiritual Ray if it gave the highest amount of potency? I think something was lost in translation.

The moment the detrimental effects of Blissful Sacrificed are removed, all thinking required evaporates.
As mentioned in the OP, Enduring Faith stacks are lost when Blissful Sacrifice expires or is cleansed through Exaltation.

What does this mean? So you can cleanse the stacks that give you your DPS combo if you want to heal yourself back and give a small shield to all allies. Why would I do that?

Drought is meant to be an offensive maintainable buff.

Wind + Earth takes 7 stacks of Faith. You get 2 stacks every 30 seconds from Benediction. If that's the case than every 120 seconds you can cast this. This is not a sustainable heal or buff. Even if it was, why would I use it when I don't need the extra healing? Wouldn't I be better off spamming Spiritual Ray as much as possible? Am I missing something here?
Spilled Blood has a chance to be gained from your DPS skills. It is spent by those same DPS skills as a 10% heal to everyone. Cool. But why? There is no way to manage when you will get a stack, and you're going to use these buttons for DPS anyway, so this just seems a little tacked on.

[SirShady]

Seraph Strike is meant to ease the obtainment of the Tree of Life buff as with no stacks of Blood Spilled it will cost 60% hp and 30% of max HP reduction for a short time.
Spiritual Ray is meant to be a rewarding DPS spell for figuring out how to survive despite using five stacks of Blissful Sacrifice.

Ok, yep. Definitely missed something here. Where am I getting all these free Faith stacks from? Why are we leaning into this self-harm playstyle for White Mage?
How would you ever be rewarded by this? Fight design in this game has huge amounts of unavoidable damage. If you lowered your max HP that much you'd get yourself killed to many late-game mechanics. Also, I think I finally see what's happening here. So you can spam Blissful Sacrifice multiple times to continuously lower your max HP, deal damage to yourself, and get more Faith stacks?

Again, why? Why am I killing myself to do my basic DPS rotation? Thematically it doesn't fit, mechanically you'd be killing yourself all the time in order to squeeze out as much DPS as possible which is counterintuitive to the entire healer identity, and you'd actively have to not use it for certain mechanics that target healers or you'd end up screwed.

Lastly, I decided to use HP instead of MP as we already have an oGCD that synergies well with self-detrimental status buffs - Lilybell. And we can hopefully look forward to the implementation of more oGCDs like it.

Lily Bell is on a 3 minute cooldown my dude. Its niche is being used on raidwides that hit multiple times. And you'd still have the max HP debuff. And again, I ask you, why is White Mage killing itself? Why would any healer have to constantly risk their own safety, and vicariously, the team's safety, in order to use their toolkit? Where does this fit in thematically to the straightforward nature/light mage identity?

[Katoar]

Why would I ever hold onto all these stacks to use a heal over time when I have a superfluous amount of heals in my kit already and can instead go for Spiritual Ray or Seraph Strike? Why would I ever go for Seraph Strike if building up to Spiritual Ray does more overall potency?

You are not going to use all five stacks to go for Spiritual Ray right of the bat as this will leave you at 1HP with 50% reduced max hp for a considerable amount of time. Tornado, Water III, Earthquake and Spiritual Ray are spells that cost Enduring Faith stacks. These stacks are obtainable only when Blissful Sacrifice is active.

Spiritual Ray is a channel with extended GCD recast time to prevent people from using Swiftcast for it. A channel as it allows for slow movement which allows adjustment.

Again, why? Why am I killing myself to do my basic DPS rotation?

Healers prefer to manage HP bars. As WHM arguably has no resource management, choosing HP to be the resource they manage in order to get the best out of the job, doesn't seem too outlandish to me.

Where am I getting all these free Faith stacks from?

Benediction
Type: Ability
Cooldown: 30sec
Cast: Instant
Range: 25y
Radius: 15y
Effect: Cleanses all debuffs on nearby party members.
Additional effect: Applies five stacks of Blissful Sacrifice to self for 5 seconds.
Blissful Sacrifice: Upon activation, extends remaining duration by 5 seconds, afflicts 20% of max hp damage to self and simultaneously reduces max hp by 10% while under the effect of Blissful Sacrifice. Gains 2 stacks of Enduring Faith.
Enduring Faith: Allows for the execution of Exaltation, Tornado, Flood/Water III and Earthquake. Effect expires with Blissful Sacrifice.

Wind + Earth takes 7 stacks of Faith. You get 2 stacks every 30 seconds from Benediction.

No, you do not get 2 stacks every 30 seconds. You can get between 0 and 10.

Making one of White Mages GCD's take longer serves no purpose and doesn't fit its identity

As WHM has no identity or if it has one it is Glare, I do not see a problem in suggesting or giving a new one. The game initially portrays you as some sort of conjurer who is attuned to the forces of nature and uses them to defeat adversaries and heal allies. And then as you level up White mage becomes that sparkly white girl out of nowhere.
WHM has no unique traits. Benediction is an old and outdated oGCD that has outlived its purpose and value. AST has the same cooldown and AoE version of it.