Mass pulling is the standard in this game, however what ends up happenning is candy men see Tanks mass pulling and then when they try and do it they forget mitigation. Mitigation against trash is more important than mitigation against bosses. For some reason Invuns are like kryptonite to some tanks.

For the first mass pull they should be using Rampart, Arms Length and Reprisal. For the 2nd mass pull they should use the 30%, Reprisal and then Rampart should be back soon. Minor Mit from everyone should be used on both.

For healers a pre placed Regen or Shield whilst Tank is pulling mobs and OGCDs to heal them whilst you help DPS the mobs down. If you don't help DPS the mobs down as healer the Tanks could run out of mit and die. A lot of new healers fall for this trap and stand around thinking healing is more important, you can do it, but it's going to be a lot harder than just spamming your aoe button. Be sure you pace your mitigation out with the Tanks, don't overstack them, wait until you see theirs about to pop off before dropping yours so you can extend the duration. For example WHM wings can be popped when Rampart is about to fall off and then you can healer bubble the other pull or vice versa.

If you are not comfortable just ask the tank to slow down.