Especially in some of the areas where there's around 10 monsters in a (boss) mob in places like Shenzun Tunnel on the Afflicted Kam boss. It's beginning to frustrate me.
You need to be very careful about flagging your heroes. You also need to bring DP removal for the whole party - clovers, honeycombs, rainbow candy canes, etc. Each area in Factions has one very difficult boss party, with the rest of the area being easier to handle.
Second, in some places you have to be careful with aggro. duh?
I found in the really harder spawn areas, setting up (micro) spirits and then flagging all H&H back except a MM (somewhat flagged more forward than the rest) works like a charm. Let the baddies spend themselves on the fodder and then charge in and AOE them.
I usually bring an SoS, MM and a Panic Mesmer for shut down. Well, at least recently anyways. 2 healers, earth and whatever henchie for the last spot that strikes my fancy at that moment.
Most of Cantha isn't too bad. Get a friend for the City areas as the eles there hit hard if your heroes are in a pile. Pull and flag, you should be fine. If doing the VQ title, you should always have DP removers just in case.
Spread heroes out against afflicted due to RoJ & the eles. Bring Pain Inverter to destroy the monks, time it so it hits right at the end of roj, and hopefully will kill them in one or 2 pulses. The focus all damage on rits.
I never had a single issue with HM in cantha. It was the easiest to vq and guardian.
I'm running a modified Spiritway-Heroteam and had absolutely no problem in Cantha except for areas with Jadebrotherhood in them. If you don't flag your heroes even 2 Knights and 1 Mage/Ritualist can cause some serious trouble :P.
Though after i got wiped once or twice due to overaggroing and false target calling and began to flag heroes i had no trouble anymore.
Rest of cantha is pretty easy, the hardest thing was to stay focused because some areas were just simply boring...
Jade Brotherhood was the hardest imo. Need to spread heroes and pack party wide healing and damage migitatrion, although spreading them can be hard at times in tight corridor areas.