I think "darker and grittier" is usually the opposite of substance, or rather, I think there's a tendency for writers and the like to think that darker and grittier means more substantial. But dark and gritty is an aesthetic, and nothing more. Like Dragon Age, the series that thinks blood and sex make a story mature, or, for that matter, the Nolan Batman movies, which sidestep the question of how to make a convincing villain by instead telling us that some men want to watch the world burn. No, I think in practice adding darkness to Star Wars, a franchise that's already truly awful, would just turn it into the middle schooler that takes up smoking cigarettes to appear cultured.perhaps make them a bit darker and less one dimensional.
Give it some substance, some grit.
But dark and gritty is an aesthetic, and nothing more.
Dialog, plot lines and character development can all be dark and gritty. It's not just an aesthetic.