Grossman isn't a dick. René Wellek was a dick, and Grossman just never learned better.
Let me explain. No, that will take too long; let me sum up.
René Wellek was a professor of comparative literature at Yale during the second half of the twentieth century. He was primarily a literary theorist with a foundation in nineteenth-century literature. He also had a firm grip on the curriculum of the comparative literature programs at Yale from the 1970s through at least the end of the 1980s, and his influence remains discernable in course descriptions even today. Above all, though, Wellek's primary failing as a critic and theorist was as is all too common a tendency toward self-reinforcing conclusions that extended to inferences about individual authors... particularly regarding the rise of modernism.1
Ah. Here's the crux of the matter: Wellek and, based on the comments Grossman has made in both places, Grossman was wrong about modernism, and in particular the problems raised in balancing "plot", "character", "theme", and "environment".2 The consequences of the fundamental error come through rather strongly in The Magicians a decent enough book, but reflective of the common failing of literati "slumming" in category fiction (not recognizing that others have met and explored solutions to certain classes of writing problems found in that category, and are therefore worth learning from) and undeserving of the praise showered upon it from Certain Places and in Wellek's own writing. This is an extremely complex issue, but the simplest (and least-misleading, but still at least somewhat misleading) statement of the issue is "The value and accomplishment of a work of literature depends more upon how its constituent parts are integrated into a whole than upon the care lavished upon those constituent parts."
It's quite ironic that Grossman spends so much time defending the inclusion of "plot" in the novel, when The Magicians has almost no real plotting in its first two hundred or so pages: There is but one "plot element" that is essential to "plot" of the concluding third of the book, in one ten-page section. Instead, Grossman spends his effort on character development and, to a much lesser extent, environment (with the occasional nod toward something resembling theme and plot). Thus, in its own way, "nothing happens" until the McGuffin comes along: the ability to actually (or, at least, potentially) reach Fillory.
At least Grossman has the good grace to admit to a couple of mistakes in his WSJ piece. Now if he'd just apply those lessons to his own fiction... and escape the baneful parts of his Yale comp. lit. background... he might write something really worthwhile, instead of just better-than-the-average-cookie-cutter-series-novel. Points for effort, but not that many for execution.
- Although I had no personal experience with Professor Wellek at conferences or the like, I heard many tales from those who did have such experience of his intolerance for being challenged on the data supporting his theoretical constructs and overneat conclusions. This, too, fits all too well with what appears to be going on, in a reflexive sort of way; cf., e.g., James Hynes, The Lecturer's Tale.
- Which are most emphatically not the things that one learns about writing sixth-grade book reports. I won't bore you with a long theoretical diatribe that, ultimately, doesn't answer the question; I did enough of that in grad school.