I use a hallowed ground spec and I found it helped a lot more because I tend to use consecrate a lot on Ryholith. Granted, I'm not pushing Hardmode of him, but should be about the same. But I think it also helps that I have 3 hunters in my 10m group and they all throw their MDs onto me before opening up 24k+ on the adds. Using a single tank.
What I do is throw my shield (dazing shield glyph) at the first 3, then judgement the other, and taunt any that go to a healer right off the bat. Then hammer them, holy wrath, consecrate and by that time the Hunter's have em dead and stuck on me due to 3 MDs.
Are you using Inquisition? Are you using the priority that I outline in my guide (see the signature)?
Aye, Inq is up 100% of the time and I am using your rotation, or as close to it as I can keep in combat.
The hunters tell me that after they have done 2x multishot they have to switch to single target dps to recoup their focus. I can understand this to an extent but what troubles me is the boomkin. I have no idea why he is pulling off me as he has said all he uses is starfall and shrooms.
Shrooms are massive threat. So is Starfall. And your AoE (Consecrate) isn't mobile.
Easy solution: Swap jobs. Make the bear tank hang onto the Shards. You handle the Sparks.
We just downed the thing on 10s this weekend with me (a bear tank) doing the solo tanking job, and one of the things I noticed was that whenever I was trying to corral up all four adds, one of them would be missed by the first swipe, and go after a healer or DPS. I had my DPS trained 'if it's on you, bring it to the raid marker I specify* instead of running away and I'll pull it off of you.' The boomkin sets up said raid marker with shrooms, and as soon as I get the Shards on the spot, they detonate 'em. If I'm busy trying to round them up, I'm not on the marker yet, so I don't go there until I have them under full control with a few extra swipes/thrashes on them.
Most of my raid Vent callouts were along the lines of "New shards, going to nacho. New Spark, going to X. New shards, make a hole, going to diamond with them, kill the Spark first."
* I have four raid markers: west (Box), center (Nacho), east (X) and south (diamond) relative to the starting point. Since I see where the volcanoes are being laid, I try and take my adds to the spot that has the least or no volcanoes to tank stuff, and two healers plus all the ranged stick with our bunch.
Your hunters need to use MD every time fragments spawn, if only one or two fragments roam and beat on your owl that's nothing to worry about. Also: you got two taunts on a short cooldown, one will bring up to three adds hitting on one owl back to you (Righteous Defense).