FDCL without the new tier set is an HPS LOSS for holy. If you don't have the 2-set then the new mindbender is still better for holy, because its the same mana regen and less GCDs lost.
FDCL becomes the top talent however the instant you get the new 2-set. Why are you even testing in the PTR without the new tier sets anyway?
Once you have the tier set, I don't care if the boss is throwing the kitchen sink on your raid you better use up those FDCLs, because everytime you cast one or two of them you get a massive PoH incoming, which is a major HPS gain. The harder the incoming damage the more you need to use those FDCLs.
@darkener and nobodysbaby: You are clearly using FDCL wrong.
a) You only need to use 1 FDCL every 13s or so. Wasting additional FDCLs will not really set you back compared to mindbender. You can afford to waste a couple of procs instead of losing HPS at key moments.
b) FDCL requires more attention. You can't just spend the proc when you get it, even with the 2set. You have to plan around legendary meta procs and the groups you are going to PoH.
Here is the correct way to use FDCL during high HPS phases:
No tier set: Use the proc on the lowest healthbar you can see when the following conditions are satisfied a) PoM is on CD and no DI b) CoH has been used or will overheal c) PoH will overheal. Although you might think that pre-casting when the heathbars are full is a good idea, it is even better to have a fast PoH to use reactively instead and FH the low health targets with little overheal. d) Legendary meta has not procd. If these conditions are not satisfied don't use FDCL even if you have 2 stacks
+2p set: You want ideally to use two FDCL procs, but with the 2 sets you don't want to waste procs if possible. Thus if you get a 2nd stack unload them both on he lowest health targets you can see (unless the legedary meta has procd). If you get one proc then the criteria (a)-(d) apply. Criterion (d) takes precedence though. Use glyphed binding heal or at least a spell costing mana during legendary meta procs even if you have FDCL stacked to 2.
With the 2set though there is a caveat. If the raid damage is extremely hard and you are in a fight to save your raid, then FDCL procs come second in priority only to PoM/DI procs, so use them right away to raise your HPS. FDCL procs are actually extremely good during high damage phases, because it adds an extra spell to heal people who took too much damage in addition to PoM and the best part is that it actually buffs your HPS to do so.
Just think of how many times you see someone at extremely low health during bursts and you know that a PoH or CoH won't save them. Casting an FH for free and gain HPS while doing it is just insanely good and it would be worth it even if FDCL had significantly lower mana return compared to mindbender.
Just think of it you are gaining a 50% bonus to PoH per serendipity stack ATM. If you think about it with the new 2set, you are gaining 1.15s from Half a PoH every time you cast an FH and on top of that you are getting 0.46s off the castime of your next PoH too. That means the FH cast not only does not cost you any time, but it actually gives you back 0.1s per cast. Although the gap between PoHs is raised by ~0.9s, your second PoH is 1.5 times larger. In essense, you get the healing from the FH and you get 0.1s of extra casting time too. It is just too good to pass under any conditions of very high damage. Even if the FH healed for nothing, it would still be a gain in HPS.