Yep, they aren't going to be easy. Last week I did Thrall + 1 corrupted zone on both 5x Druid and 1xTank/3xDPS/1x Healer comp and it was fine.
I made a huge mistake though and went with the solo talents instead of the group talents, make sure you pick the right side. It increases your sanity from 1000 to 1750 after 3 points if using a full 5 person group. If I had the full 1750 sanity bar, I could have done both corrupted zones or potentially one of the lost zones.

One thing I read and I am trying to verify, is that if you add a tank - the mobs hit harder and if you add a healer there needs to be things to dispel. Because I've watched videos of players doing 3 man teams and the mobs feel super squishy and don't hit hard at all, whereas in the full 5 person group some of the aoe move takes half the hp from my entire team.
So hoping to get a better answer on that one.

There are groups out there that on the first week cleared the entire zone, with no masks but still - impressive feat.