Dunno about Gwynnega but my experience matches that. Also I think it's easier to line edit as you go. Big Stuff often required a full read through, a pause to get enough distance to see it in perspective, another read, and maybe a conversation -- and people in classes often don't have/take that time with each one.

Big stuff is also much easier if you can get in sympathy with what the story is trying to accomplish. In my workshops, there were so many stories so alien to me that I wouldn't have trusted myself beyond the turn of phrase level, because for me to like it it would have to be turned into some other story altogether, and I lacked enough context to tell whether that is exactly the feedback they needed, or whether it simply wasn't meant to be the kind of story I would ever like.