I'd think the average man would end up losing more than just a few marks. I know I'd have a damn hard time trying to pass a top Spanish (in fact I believe I'd pass a C2 English certification much easily than a C2 Spanish certification even though Spanish is my native language)! Heck, I see English natives writing "your" instead of "you're", don't tell me they'd get a
CPE certification
The thing is, when you start primary school you aren't taught how to buy stuff from a local store because you were taught by your parents, by imitating, by looking. And if you are doing it wrong you aren't corrected. Then comes an exam that asks you the right way of using a verb and you just answer with what you know. In English it might not be that noticeable because Spanish has 3 persons, tenses and verbal moods, aspect, number and voice which end up in 10 different conjugations for every verb, each to be used in different situations but some of which are just misused (for example, very few people use the future tense, most use what would be the gerund, that's, virtually nobody says I'll go to the cinema, people just say "I'm going to..."). A native just doesn't care about the difference, but foreigners are taught to care about them, so eventually a foreign guy studying Spanish would have better chances of passing SIELE or CELU than a native. What happens in that video with Japanese would happen for English native or for Spanish native with advanced tests in their own language.
Down here, as a different example, there's actually quite a lot of buzz because young people don't understand texts. They reach college without comprehending texts. They can read it alright but they get confused when asked to say whether that paragraph was about X or Y. And that's a good chunk of any exam.
Regarding names again, I used to follow female idol groups so ended up learning probably a couple hundreds different female names. Some of the odd ones I can't write but I can read immediately. However, I wouldn't be able to say if that was a fast process or not, I never actually sit down to memorize them but instead learned them by
osmosis after associating their faces with their names and then with their name tags.
There are worse tests than N1, take kanji ones like
Kentei for example. There are whole TV programs aimed at kanji writing. And back when I watched them japanese people who passed
Kentei 1 were hard to find, especially in the entertainment business.