Yeah, not training this when you are young is a really bad idea, especially for some of us who start with negative Social dots by the standards of common society
I suspect Amu actually did in this quest, owing to the... "non-standard" nature of her mind. Since personas without the capital "p" are apparently meant to be a natural development formed via human interaction (along with small-letter shadows), her somehow having her persona getting torn apart exposing her Shadow implies that she got stunted somewhere along the line, until she "regained" her persona (or 3) through her Charas.
After all, Shadow Selves are meant to be incapable of lying and not intended to be exposed to other people - so if Amu's main self was a shadow, she wasn't playing with a full deck hence her needing to have "learned to do things shadows simply aren't meant to do".
I suspect that Ami, Micchan and everybody else with the yellow eyes in her year is also in the same boat - it's just that since there are no social expectations for them at that age, they currently perfectly fall in line with what typical 7 year olds are meant to have for Socialize skills, which is no dots.
Their exposed Shadow Selves I speculate got caused by that questionable classroom social dynamic of discouraging each other from keeping secrets, leading to either them having torn apart their own personas or simply never ended up developing one in the first place. Ami's midly-sinister suggestion on dealing with the reporters might have been part of a Shadow Self's naturally aggressive instinct to lash out (which is the sort of behavior that does automatically makes you enemies everywhere you walk).
For Nocturne/DeSu2 veterans, what does this mean in practice OOC?
Nothing actionable, I'm afraid (though bear in mind, I'm not sure I'd call myself a veteran).
JP's doesn't even exist in Nocturne, the whole organization only appeared in DeSu 2.
Best guess, it means Polaris doesn't exist and JP's had no warnings about any Septentriones and Hotsuin has never met Alcor.
Or it could just mean he hasn't met Alcor, but Alcor and Polaris nonetheless exist though they will only become relevant if Hikawa is stopped from executing Conception, being the QM's "backup plan" on how to end the world if we stop the first attempt.