It's possible that you're not being dispelled when you should be and the healers are sitting on their dispels. However, healers now have an 8 second CD on their dispels, so if multiple people are debuffed it needs to be triaged and hopefully two healers don't choose the same person.
<< has five healers.
I know there's a dispel CD. I typically get these runs with like 3 or 4 priests and apparently not a single freaking one of them know how to Mass Dispel.
As it is I use my fear break/magic dispel(depends on who I'm on, really) on CD. The fact that I can look at those trash packs in Recount and see 0 dispels coming from the priests is appalling.
Same goes for the three fish guys in Terrace. Two priests and myself. Both shadow. I was the only one dispelling cleansing waters. Really guys?
However, it is very expensive, so it's not generally used to clear just one or two debuffs, and using it on CD will seriously tax mana reserves. One place you will see a priest spamming it is LFR with the trash mobs you mention which put a stacking petrification debuff on the raid. But it has a target cap of 10, so even if I mass dispel where you are, it may not dispel you. And all bets are off if the tanks pull the next pack without waiting for stacks to fall off and healers to regain mana.
Mass Dispel removes 100 effects. If it hits *half* the raid, all at 8 stacks, it should remove enough to not cause issues for the next 15 seconds. And I know how mana intensive it is. See: I have five healers. One of which is a priest. Spriest can also use this spell.
I tend to get runs where no one dispels ANYTHING and then our Druid tank gets petrified, rocked, and then the healers complain that "tank sucks" when the only damage mitigation a druid gets is Dodge.. which you can't use while petrified.
It shouldn't be difficult. It really shouldn't. And people should really be killing those Jinyu before the petrify guys. They transfer health to the big guys, making the big guys take longer to kill. They die *fast*.