Bill Zebub
“It’s probably Matt Mercer’s fault.”
Speaking of my experience, absolutely not. If they'd only been far enough along the Dunning-Kruger curve to recognize that if they wanted to run with little to "no prep" to buy any sort of prepared adventure or campaign to run, they wouldn't have been terrible. Rather, they invariably think that they can get away with no prep because they think they are really super creative people who can improvise great adventures on the fly. They are on the peak of Mt. Confidence. No one here is giving me that vibe particularly because everyone here is talking about running something that is the equivalent of buying hours of preparation and is usually designed to run with relatively little preparation. That in itself guarantees at least a 'C+' sort of gaming experience.
To get down to 'F' you need a lot more confidence than that and either "no prep" or "All my prep is in the form of a short story and I don't follow the system rules."
So...that is reading to me like a criticism of those GMs, and not of the general idea of zero-prep dungeons. No?