Personally I would peg him as a highly over-rated writer who is nowhere near as clever as he thinks he is.
I don't think he thinks he's a particularly clever writer, he thinks he is (and actually is) a very canny businessman — I think he views his books as product and constructs them with great care (albeit cynically and with very little 'art'*) to hit his target market, both within the comic medium and as adaptable IP for film and TV.
He's very, very good at it, but I find the majority of his work soulless for that very reason.
(Worth noting, for all that sounds like —OK,
is— criticism, I think it should also be noted that MM has a reputation for being one of the most equitable writers in the industry when it comes to sharing the proceeds of what is basically a one-man IP farm with his co-creators.)
*By which I mean, his writing is workmanlike, but feels like a careful arrangement of story beats, without any real flashes of inspiration. The
art is usually great, because he understands the value of paying top dollar to get really good artists, and how to get the best out of them. (Paying well, basically.)