Let's analyze the 2p for raiding. On my
last Mistress kill, I spawned 78 orbs and used 49 brews. With a 40% chance on every brew about 20 of those should come from the set bonus. That is roughly 25%. From all of my healing taken, I did 26.5% myself and of my selfhealing orbs make up slightly less than 50%. There probably is some component within Celestial Fortune, but I have no way to account for that at this point.
Taking all these percentages together means, 2p provided roughly 25%*26.5*50=3.3125% of my healing taken. Even if we want to account for the additional celestial Fortune heals, we might get to 3.5% as I'm currently running on very low crit. But even if it is 4%, I wouldn't exactly consider it "incredibly strong".
On the same fight, my dtps from stagger was always more or less somewhere around 400k. That means every orb reduced damage taken by roughly 200k damage (5% reduction of dtps over a 10 sec period). That means the 78 orbs removed 15.6m stagger damage. That is somewhere in the region of 4%. Which is not particularly great either. So all in all our bonus was more of "feel good" bonus (which is a good thing) and not as mandatory as many of us thought it was.
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That depends, is 3% more healing on you and thus 0.5% more healing overall (still looking at the same log, if you have wildly different results please let me know, it is a small sample size) worth 0.3% more damage overall? That doesn't take into account, that the rotation gets a lot more fluid and efficient with the shoulders. I'd say this seems like a fine trade.