I mean, he's even said it himself, the most recent Mistborn trilogy was not an attempt to further epic fantasy, but a different experiment all together. It's an exploration of different types of stories, but within a universe that was familiar.[0]
I think the jury on the Stormlight Archive series' care is still up in the air, considering what makes the original Mistborn Trilogy so great is how complete the story is, and we're only 1/5 of the way through SA's arc (with what, another 20 years left until they're done)?
I don't think stories need to be deep and epic to be fun and worthwhile. And while Rothfuss may write the most beautiful prose (and to me, he does), it turns out that I'd rather have quantity with above-average quality than a couple of masterpieces with supreme quality.
But hey, to each their own. At least we're reading things we find interesting. :)