Haste, mastery and spirit are much, much worse than crit when it comes to dps. You can clearly see it when you look at the damage done by mindbender (which you would choose over shadowfiend, of course). I don't really trust your math, so here are my own calculations:Well, haste (which increases RPPM effects such as the legendary meta) and mastery aren't all that much worse than crit, particularly with crit stacked as high as yours. At 28% crit and 15% haste, I'm already at a point where getting the next Shadowfiend breakpoint from haste is more valuable than an equivalent amount of crit. But let's assume crit is 30% ahead of the worst secondary (a generous assumption; they all get closer together as crit rises). To cover a gap of 4.6% damage, nevermind the healing, you need to gain around 15.3% crit or 9.2k rating by wearing off-tier pieces instead in order to break even with the loss of the set bonus. That looks like a "no way in hell" sort of number. Then recall that you can reforge undesirable stats on the tier. So that would leave it only 21% ahead of the worst secondary, needing a whopping 13k rating to break even. That's more than your total crit. From only 4 item slots. That's not happening. Ignoring tier will be a mistake if the bonuses go live as-is. Even more so for non-atonement priests who gain even more benefit from the set bonuses.
Assuming a 45% crit chance (which should be easy to achieve next tier), with the set bonus this would become 55% crit chance during archangel. Assuming you usually hit for 100k non crit your dps would be 155k (versus 145k).
155 * 18 = 2790. 145 * 12 = 1740. 2790 + 1740 = 4530k over 30 secs.
145 * 30 = 4350.
4530 - 4350 = a 180k damage gain every 30 seconds.
But, you would have to lose your evangelism stacks. Since your crit chance is at 55%, 155 * 0.04 = 6.2k. 6.2 * 15 = a 93k dps loss.
180 - 93 = still 87k damage.
(87 / 4350) * 100 = a 2% increase in dps.
But, with eva dropping you will have to pay more for your atonement spells.
Assuming a penace - holy fire - smite - smite - smite - penance - smite - smite - smite - smite rotation, you would use 7 smites, 2 penances and 1 holy fire each sequence.
(7 * 8100) + (2 * 11160) + 5400 = 84.420. 84420 / 10 = 8442.
8442 * 0.94 = 7935. 8442 - 7935 = 507 mana for each stack of evangelism.
507 * 15 = 7605 mana or 15210 mana each min.
So, you would gain 2% dps at the cost of 15210 mana each min. I'm not sure how much spirit you would need to counter this loss, but on a 10 min fight, you would need an extra 152k mana! To get a 100% dps increase (if that were possible) you would need an extra 750k mana every minute, that's how ridiculous it is!
10% haste at a 25% uptime would be 2.5% haste on average. That's like having 1k extra haste. Not very impressive imo. It's defo not gonna give you 2% extra dps (or 4% extra healing for that matter).
Getting the tier pieces will get you loads of mastery you defo do not want. There's only crit on the chest. Even if you reforge some mastery or spirit to crit you would still lose close to 2k crit. If Blizz is gonna give us thunderforged gear again, I'm very sure it will not be worth it at all.