We have been doing this fight in hc mode from about the 3rd week it was possible to do hc. (So not world 1st by any means).
For our first kills we found healer dps to be vital.
Until the 1st totem pops and during bloodlust we use one healer to heal and hybrid offhealing (druid NV, HTT from shaman or VE from spriest- they only do this if needed and it rarely is). The other 2 healers dps from start. (3 healing is totally viable). Our resto druid in particular does over 100k dps with prepot and blust (HoTW talent) and even though he doesn't cast another dps spell the whole fight it is a LOT of damage. Disc and mistweaver can obv dps much of the fight. paladins and shaman can also do nice damage over the course of the fight.
People with the link debuff NEED to use damage reduction cd's.
During the final burn phase make sure you use ALL your raid cd's (AMZ, smoke bomb, barrier etc etc)
Make sure your healers inside spirit realm heal themselves enough for mana regen but maximise what they need do on the dps. personally i top myself 1st and then spam the dps refreshing my own buff with a HoT near the end. gives me plenty of mana and plenty of uptime on my personal buff but making sure the dps are well over 20% on theirs.
If you are all over 490 ilvl then you are 15-20 ilvl over what the top 1000 or so guilds needed to kill this boss. This is not to be demeaning but to let you know that all your dps could up their game. are they all using 2 pots/pull on progression? 300 food?, flasks? gemmed and reforged correctly? doing their rotation/priority optimumly? If you think the answer is yes to all of these you are very much mistaken.
Anyway. try and up the dps a bit, use cd's, get the healers to do a few million each ( i think i did about 4-5 million damage on this boss when it still mattered what i did).
It is often useful to make everyone in the raid responsible for suggesting what their class can do for a fight. I do a lot of PUGs of this tier on my alts and am constantly amazed at how little people use their class utility. There is some trash after spirit kings that stacks a move slow debuff that when it hits 10 stuns you. everyone seems to know that mass dispell gets rid of it but i see a lot of shaman that don't know they have totem (talented) that also gets rid of it and a lot of druids that not only don't know that stampeding roar gets rid of it but they can reset it on themselves by shapeshifting. Also mages can blink from the stun and dk's remove stun with IBF.
And don't even get me started on the people that don't utilise symbiosis to it's utmost.
I hope the 1st half of this was helpful and that u forgive the rant in the second half