We also had some issues with the adds on the first kill.
Here's how we do it.
DDs and Healers stack on the "platform" behind the boss because it's very big. We did not really get any problems with the "voids" of the sha bolt.
The 1. tank pulls and tanks the boss on the platform right to us. After the 1. corrosive blast, there's a tank switch and the boss tank just stays on the main platform of the healers and dds. That's possible, because the boss will swirl now and the 2nd corrosive blast will be maybe 20 secs after the swirl.
This brings you some advantages:
1.) If you have to "avoid" the swirl, especially as a healer, you will never get any range problems to the main tank
2.) The current boss tank can also try to get some of the adds or even dps them if the other tank pulls them near the boss.
3.) If you cannot avoid the swirl, use some personal CDs or just run to the "entrance" to the fallen protectors OR run through the swirl (means to the right as it goes clockwise) and you will only get one hit.
Right before the 2nd swirl, the 2nd corrosive blast happens. So make sure that the tank leaves the platform to the right again. The adds should be (almost) dead, now.
Our dds stack up to 4 debuffs, some heals also try to get 3 or 4 as this not really much damage. Tanks also 4 or 5, but more than 6 seems too much. We have prot warri and blood dk or druid. Positioning was the key for us.