Quick: what do you know about Isaac Marion? Probably a) he's got a YA novel called Warm Bodies about zombies. b) And now we know how he really feels about young adult as an age category.
Here -- read this post from Read Now Sleep Later.
Isaac Marion, how can you say YA is a category full of books without substance, complexity, style, mature themes? It's for teens to read about teens with agency, as Tamora Pierce said. The Book Thief. Patrick Ness's Chaos Walking trilogy. Swati Avasthi's Split. Substance.
Who's to say, anyway, that the only good book is one with substance? Huh?
I don't think you know what you're talking about. Oh, and by the way, I only picked up Warm Bodies because it was shelved as YA, and I have an inkling Summit optioned it partly because of its potential appeal to the young adult audience. Guess you want your money back now, eh?