I play with 2 specs the Both the Deep wounds spec and a spec more designed for survability.
The first try after the gates opened I used my threat spec underestimating the swings the boss would take at me we were still new to the fight so we did wipe and I was one of the first to die I swapped specs and it did make a big difference and with more practical experience of the fight and in particular with improved demo shout this made the damage far better and we killed it that go.
Someone thing else that made a big difference was using a cooldown at the third inhale as this is were the damage ramps up with also if needed using a trinket when you taunt just to help with the change overs.
A few other things that might make it easier not all ranged have to stand at range just enough to stop the debuffs from being used on those in melee range like shadow crashes on general.
This means you can keep your main tank healer stood with melee so they dont have to move rather than running around.
For a tank its all about surviving as due to the damage buff you gain threat isnt much of an issue. even if that is the case it would be near the end after the final Exhale as im not sure if its the same on 10 man as we didnt have a dps problem but in 25 man he onlky has time for 2 exhales so you can spread and nuke after the 2nd and ignore spores, (slightly off topic I know but it was a big help for us to get it down in 25 man)