I was reading this thread yesterday before I left to go to a club meeting. I got there early so I could study for N2 a little bit, and one of my Japanese friends stopped to chat for a little bit before going to class, so I showed her some of the grammar problems I worked on the day before (which kicked my ass, to be honest). For the record, this is from the 模擬試験 第１回 in 新完全マスターN2 文法 book. These are the two questions she tried:
1) 就職する（ ）、林先生には大変お世話になりました。
1 において 2 にあたって 3 にかけて 4 にともなって
2) このメーカーは、デジタルカメラや携帯電話（ ）製品を多く作っている。
1 という 2 といった 3 とする 4 とした
She never gave me an answer for the first question before asking me what the right answer was, so I don't know if she got it right or not. For the second, she narrowed it down to "という", "といった", and "とした" before narrowing it down further to "という" and "といった". After forcing her to pick one, she decided on "といった" (the right answer), but was still adamant that "という" could be valid as well. In this girl's case, judging by how much time and debating she had to do for both questions, she would probably run out of time before she could answer everything on N1.
My other experiences have usually been showing friends a random question from the reading section that I got completely wrong and couldn't figure out why my answer wasn't right, so I would ask them what they thought the answer was and why my answer wasn't right. *Almost* every time they gave me the right answer but sometimes they would also say that the passage/problem was worded to be intentionally tricky and why, then try to explain why my answer wasn't right.
Overall, I'd say I have as much faith in a random Japanese person being able to pass the JLPT N1 as I do a random American being able to pass something equivalent to JLPT N1 for English. I can think quite a few people off the top of my head that I think would probably struggle to pass an equivalent English test, and I can also think of a lot of people who I think wouldn't have any issue with it.