(Apologies if this is a dup bug; I crashed trying to submit first time).
The DPS of 4-dot mobs is way too high, more like a raid mob than a group mob. I sent my L19 cleric up against one of the (blue) ants at the Zihurr Hive and didn't last 10 seconds, despite constant heals. My L16 paladin tried one of the (green) 4-dot spiders at the entrance to Kegor's End. The mob did 3128 points of damage in 11 seconds, and I only lasted 11 seconds because of lay on hands and my racial ability that blocks all damage. I have a little over 2K HP and had only a sliver of health left when I ran.
In release most of my characters could solo a green 4-dot and my better classes (disc and rogue) could do even-con 4-dots most of the time. I would not even be close now. My paladin would require at least 2 healers chain casting heals to be successful.