First I think the lily mechanic is a great way to start giving White Mages an identity rather than leaving them the bland baseline healer they are now. Both Astrologian and Scholar are defined by their take on random mechanics (cards and crits respectively) but the WHM has no defining mechanic.

Lilies as they are implemented now, take WHM in the direction of AST and SCH by adding in a random mechanic. This is counter to the idea of a “pure healer” as one would expect that healer to be the most consistent and predictable. That doesn’t inherently mean the mechanic has to be uninteresting though. If we had a more controlled manner of generating and manipulating lilies where our spells had synergy and interacted with each other, the class could be both straight forward, consistent and have more depth, which it desperately needs.

Below are a few of the changes I would make to carve out the WHM identity and create a more interesting and dynamic “pure” healer.

1. Regen should perform the same heal over time function that it does now, except when it expires it generates a lily. Now you would want to have a way to tune lily generation so having an internal cooldown of 6-10 seconds would mean staggering your “Regens” and managing when they expire to generate lilies would become part of optimizing your healing (depth). A variation on this would be to have a lily generated every X ticks that successfully heal a target (overheals wouldn't count).

2. Secret of the Lilly II should be moved from a chance on a crit to a mechanic that triggers when using an abilty that consumes three lilies. That way if you use the ability because you absolutely need to then no cooldown reduction but if you can hold out for the third lily (more predictable without the random aspect) then you get reduced cooldown on Assize and Asylum.

3. Divine Benison should move away from being a shied which has more SCH flavor. Instead having it be an ability that converts the next single attack on the target that does 25% or more of the targets health in damage to a damage over time effect that deals the same damage but over 10 seconds. This keeps the WHM more of a pure healer and makes logical sense with the HoT nature we are using as the identity of the WHM. It also removes some of the sting from having stoneskin removed just to be given a shield back that feels worse all around.

4. Utility should be added to WHM through the use of abilities when at max lilies. As example having Assize refresh all HoTs on party members in range, having Asylum split damage amoung those in its radius when cast at three lilies, or assize debuff all enemies hit when cast at max lilies. Things that are still very straight forward and have a low barrier to entry but have the ability to be min/maxed at higher levels of play.

5. The reward system of lilies needs to be addressed as well. Cooldown seems like a poorer option than having a percentage buff to spell speed. That way you could get to full lilies and then when dpsing you would be able to pump out more dps but have the lilies degrade after casting multiple non-healing spells. It then becomes a pro/con evaluation of how best to order the use of your abilities that use lilies because of your ability to generate them through regens you could set up to have a decent burn phase with smart play or a smaller burn phase while still being able to drop a 3 lily spell afterwards.

These are just some of my ideas that I feel would create a more interesting WHM with depth at all levels of play and better align with the stated design goals for WHM.