The issue with haste is if you're going oom, it's not as good, often on prog you will go oom. And the reason Mastery is so good is not because you're focusing specific players, that kinda shows that you don't really get what mastery does. With 2 hots on a target, mastery is your strongest stat. On hard prog, cultivation is your talent on the majority of fights, on hard fights, people need their healing most when they're low on hp, aka under 60%, where cult will proc, and during that time Mastery is very strong. Then you add on Spring blossoms for most fights where people are semi-stacked, adding another hot onto anyone low, and you'll have 3 hots on anyone dipping under 60%.
Most of the community severely undervalues mastery, because they consider the parts of fights where not a lot of damage is going out, but that doesn't matter, because you can heal that up very well without having to change all your stats to build around that. What part matters is when people are taking damage that risks them dying.
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https://www.warcraftlogs.com/ranking...est#metric=hps
There you go, check his talents, you can find a place for it on the majority of fights. 21.6% Mastery.
KW is a damn god, he's the person I found out about the Spring Blossoms addition from.