Let me start by saying that neither the new hunters nor Behemoth are in anyway overpowered and in need of a nerf/buff.
Earlier today I was playing Behemoth and the new hunters offline and I noticed something, all of the hunters were doing regular damage to Behemoth so his health was not melting in under 3 seconds. This intrigued me so I did some testing and found that even when standing absolutely still so my crit-spot was easily able to be shot, I was taking a small amount of extra damage. Then I figured it out: neither Behemoth nor the new hunters are over/underpowerd, the online and offline damage is GREATLY skewed. Later I was playing with Torvald in an offline game of defense and I noticed that even when all of his mortar shells hit Behemoth, only about one bar of health disappeared instead of 4. I also noticed that Behemoth does more damage per melee offline but that just fits into the major damage skew online in favor of the hunters.
TL;DR: the issue with Behemoth is not his “survivability”, but a bug that skews the amount of damage that he and the other monsters give and take from the hunters.