All a thread like this tells you is whether or not you've found a good set of builds for a particular mission or been with a group that has.
For anything in PvE, once you figure out at least one way to beat a mission or boss then it's just a question of whether or not you make mistakes. For instance, getting masters on Rhilon Refuge is very difficult if you don't do something to change the earth damage to another type of damage and/or interrupt the Drought. You can get your whole party wiped in seconds.
However, if you bring the right skillsets, it's one of the easiest/quickest masters in the game to get.
I hero/hench most things personally, and there's only a handful of missions that cause problems. These are usually timed missions and/or require fighting on 2 fronts simultaneously, but most of those can still be mastered with H&H.
Eternal Grove is a pain without humans, but fairly easy with folks who know what they are doing.
Same with THK - and several other missions, imho.
S

(though napuli seems to be a bonus that eludes my characters for a while)
)