Totally agree with the OP, and it’s something I was just talking about with my best friend a couple days ago. Except we’re both Cameron fans 
IMO:
M. Night is notable for:
Twist endings that worked amazingly well once, but not so much after.
Good at creating a novel story conceit, but most of the time unsuccessful in the execution.
Aping The Twilight Zone.
Amazing directing skills.
Great with dialogue.
Terrible with plot.
Fantastic with actors, especially children.
Good and unfolding a story, but terrible at writing them.
Full of contrivances (re Signs, LITW, The Village…)
Top notch cinematography; great editing.
Subtle ambience, muted and understated.
Firm believer in “less is more” when it comes to effects and creating fear; sometimes to a fault.
Ultimately, what undoes him is his arrogance in thinking he’s a good writer, and not taking ANY constructive criticism. If he insists on writing his own stories, at least, get a good editor, or team up with a great writer. He can’t tell when his ideas are corny and overblown. I’d compare him more to Lucas here.
James Cameron is notable for:
Amazing visual effects.
Pushing technology in the film industry.
Interesting science fiction concepts, most really good, some kinda bad.
Epic screenwriting.
Mixed bag on dialogue.
Well thought out plots.
Great scores.
His passion for awe and the unexplored is usually very apparent in his films.
Fucking cyborgs.
Not all that great with actors (Eddie Furlong), but thankfully, he’s been able to just let the good actors he does cast to do their thing (Sigourney, Ed Harris, et al). Not sure where Arnold fits in here?
Over-the-top action and set pieces, for better or worse.
Decent writing, and some novel ideas.
Superb art direction/visuals (and a lot of it has come from him, and his paintings).
Iconic characters.
The catchphrases seem to write themselves.
Bombastic atmosphere, highly polished and glossy.
Bold, unafraid, and risky filmmaker in all the right places.
I believe Cameron is in a completely different league as a filmmaker than M. Night. Cameron has more muscle, overall talent and is a collaborator. He’s got unique vision, and makes movies from his passions in life. And it shows. If there’s something unprecedented he wants to achieve, then he invents it. He makes a lot of pop-corn fare, to be sure, but most often the pop-corn goes down much deeper than you think. His movies have re-watch value; M. Night’s – not so much. Every filmmaker takes some missteps, and even Cameron’s perceived missteps aren’t all that bad compared to M. Night’s. I’d take The Abyss or True Lies over Signs or Lady in the Water (haven’t seen The Happening :rolleyes: yet) any day.