Much as I love the MA stuff, and I do love the MA stuff. A lot. (Witness my Chat post earlier) but I'm not certain I'd agree entirely.
I don't mind the MA stuff. I don't mind lighter and softer, everything has it's place and time, indeed. But... There are stories that simply cannot be told using this kind of narrative style, and refusing to have those stories (many of them very good) be told isn't particularly mature either. Admittedly I don't like to use the term "mature" to describe any form of art, but I do think there is often merit in "Darker and Edgier" (although as always, that depends entirely on how well it is done, things can be done well and things can be done badly, MA is generally done well, rather than having some kind of inherent superiority in it, although I should note that light-hearted comedy is generally easier to pull of than tragedy, which 90% of the time just becomes a turd)
Now, I'm not going to pick Sandman, or Watchmen, or any other of the famous comics to show what I mean, I'm going to pick something completely different (because it's awesome). I'm going to put forward, as an example, Planescape: Torment. Arguably the best story told in game-form (although not, definitely, the best game) and I dare say that it could not have been pulled off in any other way.
Deconstruction is indeed mature: It's just that 90% of those who do it have no idea what they're actuall doing. The point of deconstruction is to look at the underlying assumptions of a genré: To see what makes it work and how, and what the consequences of conventions are. Sure, it can easily become a game of language, but at it's heart it's an attempt at understanding our own thought processes, and I really don't think that's immature.