I don't even buy this. There are a bazillion screenwriting books that cite Cameron's work. There are top level people in the craft that cite his work.
Terminator 2 isn't great because of an action scene, it's great because it has a terrific script AND good action on top of that.
He is not an average writer, he far above that. Writing is structure, and yes that is a talent, a very rare one at that which is obvious because probably upwards of 80% of the shit being made structurally doesn't work.
Just because Tarantino writes dialogue a certain way and someone else doesn't really mean much. It's like saying "well Larry Bird isn't really good at basketball because he didn't dunk much" ... uh so what? A basket scored is a basket scored, doesn't matter if the player does it one way or a different way. The point of storytelling really boils down to being able to illicit emotion from an audience and hook them into a story so that they care about what's happening and then demonstrating some kind of changed experience.
Cameron doesn't need to be Woody Allen or Quentin Tarantino to be a very good writer. Aliens, T1, T2, Titanic, even True Lies, these are not good movies if there isn't a very good script underneath, I think this whole idea that "well you can have a average/crap script, but a good director will make it greatness" is overstated by the general public. That's as well w really not how it works, 90%+ of time if you don't have a very good script, the movie is not going to work, I don't care if Spielberg is the director or not.