Yeah, unlike the spider bosses this EK is pure physical damage, it should really be in the wiki since it's hard to know without trawling the forums for the correct info. Being a phys spell it's a hard counter to evasion and being pretty much instant hit, that's where the reputation comes from. Overwhelmingly, immortal call is the best defence as demonstrated. Best to walk up to Sallazzang and hit with your best single target damage, and leave the devourers alive to get max charges from your Enduring Cry. If the boss is not devouring it goes down quite quickly.

Unless they changed it, I don't think it's EK or a phys spell. I've had characters who run grace/ondars who just don't take damage from the super shot at all, except every once in a while when it one-shots me.

And have you had spell block and/or spell dodge on those characters? It's posts like these that help make the situation so ambiguous, because you don't give the whole picture.