[Lavindathar]

The only thing I can think of, is that he means you are taking too much damage from being too close together with that many melee from Needle Spine.

But its hardly an issue, and tbh, if that is what is wiping you, you're not ready for BT. Najentus is as easy as it gets.

Needle Spine - Fires a needle spine at 3 targets, most often in a cone, dealing 2890 to 3910 physical damage to them and an additional 2280 to 2520 frost damage to everyone in 6 yards of them. He uses that ability all the time, except while under the Tidal Shield and about 10 seconds after Tidal Shield bursts.

It's hardly a lethal attack.