okay, I've gotten to the "Osteon criticizes the rescue mission" part of the VOD. I saw spoilers for this stream so I was not as struck by the reveal that Osteon was watching the whole time. Instead, I was more focused on how bad this academy is at teaching anything.
First of all, Osteon is grading the students on their ability to strategize, which is probably pretty frustrating for the students on its own given that this academy doesn't teach strategy (or much of anything really). The students are getting a pop quiz on a subject they've never been taught and being called stupid for not getting full marks. (which is not a great way to teach anything tbh)
Secondly, I don't think Osteon's critiques really taught the students much, because it seemed to me that Osteon simply didn't understand the students' perspective. Osteon was basically just grading them like this was a test with an answer key. For Osteon, all of their actions have already been sorted into either good or bad. And when explaining why they consider an action bad, Osteon incorrectly assumes a lack of understanding about the danger they were in on the students' part (ex. assuming that the students stopped on the bridge because they thought they were out of danger), which prevents Osteon from teaching anything in this moment. Every time Osteon criticizes their actions, the students have an explanation for why they made the decision they did, which can and should have been an opportunity for discussion and actual learning. Instead the students' actions just get graded as "good", "bad", or "bad but understandable" and they move on.
For example, in the case where Osteon criticizes them for letting Legundo run ahead and Scott explains that he felt that, since Legundo is the slowest, the group could get to the dock faster if Legs ran ahead, Osteon just responds that splitting up was still foolish (bc legs could be attacked while on his own I assume). The problem is not that this is an unreasonable criticism. The problem is that this doesn't teach the students anything bc they're not stupid, they knew that was a risk and chose to do it anyway. The way for the students' to learn something from this was to engage with the motivations behind their actions. Osteon could have been explaining the best way to prioritize speed versus caution, and how to evaluate which one a situation calls for, rather than treating the students like they don't understand that they could be attacked on the road (something they understand VERY well).
TLDR; Legs, Scott, and Graecie are smarter than Osteon gave them credit for and that is in spite of this academy, not because of it. And because Osteon didn't realize that, she was trying to teach them stuff the three of them already knew.