Yeah we 1 shot this without buffs and basically 9 manned it because our drawer couldn't do the patterns. Was hilarious to hear him swearing on vent when he got it wrong and every1 else was just laughing all the way through our 1st kill.
edit: pretty much the only way you should wipe on this is if you kill lu'lin before p1 is over in which case you cant reduce the stacks on suen in p2.
Yeah, we one shot Twins as well after like an hour and a half of wiping on Iron Qon. Twins are insanely easy, the only thing we used was the red crane that does damage. But that's basically only because I was healing and I was so bored (and we were 2 healing the fight) that I just told the other healer to keep people up while I did the 5mil damage.
It's totally unnecessary to use them on normal, think both me and the other healer finished with 100% mana, there's just no damage, it's really a boring fight. I purposely fell asleep a couple of times with the flowers cause I thought it might make things more interesting. It's basically just the same as LFR really.
That was with 1 tank, if you use 2 tanks it'd probably be even easier.
Agree with the general consensus here, unnecessary to use the celestials for sure. They aren't even really required on Heroic!
However, they do make the fight easier - at the very least I'd recommend doing the Crane (Chi-Ji/Red) one during P2 and P3 again when it resets at least; the additional damage gained on the boss is pretty high from it for a few seconds playing connect the dots.
If your healers are struggling then also do Wind Serpent (Yu'lon/Green) as this makes the healing faceroll - it can be done in both P2 and P3 again after it resets.
I wouldn't really bother with the other 2 to be honest. If you are borderline on dropping a healer, then just make sure you do the Wind Serpent (Yu'lon/Green) buff and you'll have no problem doing so.