Try to do a ZG / ZA group with people in full 359 who were carried to their epics and you will also do nothing but fail. Bad people in 359 gear wont out perform bad people in 346 gear.
I have done a number of ZG and ZA runs with people in an average of 346-349 gear, and the runs went quite fine. If people know the fights, and dont suck at their class, the Zandalari heroics are no harder then any other heroics, and are quite doable at the minimum entry gear level.
The only overtuned boss out of all of them is Venoxis (now that they fixed the Eagle boss in ZA to not be punnishingly hard on mele heavy groups).