The main issues I'm taking with the testing administrators and the 'hero creation system' as a whole are twofold. First, the evidence that is available, and from the MC's own point of view, is that he isn't in a real world, so to speak. He's in a kind of scenario, a simulation which is simply being replayed over and over and over endlessly by many people simultaneously. So, from the MC's point of view, its effectively consequence free, because unlike his 'ideal hero' companion in round 3 he is intelligent and is on his third run through, so he sees these people as simply not being real. It's like playing a Fallout or Elder Scrolls style murderhobo, or choosing all renegade dialogue options in Mass Effect, there are no real consequences for his decisions.
True, he didn't know about the parallel fantasy worlds on the first round, but then he already had signs of developing a borderline personality disorder being driven by ptsd at that point. We see inside his head during the third run when he meets the Saintess how he still saw the game as a matter of life and death the first time around, even when the point of the Saintess was to soften the blow. The look on his face during the flashbacks, like when we see the death of the first Lanuvel, or the flashbacks explaining the role of the Saintess, he was experiencing some pretty severe mental trauma by that point. The minute they woke him up in the second round in the exact same world and the exact same scenario at the exact same start point...
Well, I think by the reset at the start of this series, ie the start of the second round, he was already on the cusp of full psychopathy, and rage-inducing PTSD. That's why he flipped out and killed his companions the first time through. We even see it in his skills, how he has the 'berserk' skill even when he seems to be keeping his cool during fights; the MC even says his 'mind' remains the same even if his skills were reset. Look at how he treats Lanuvel on the second and third runs. He described her as someone that made his heart flutter, she's obviously a nice person and, most notably, the one companion from the previous runs the MC DOESN'T actively try to kill.
I have a theory: that the game fucked up on his first round, and Lanuvel died far too early. Her role in the 'hero' simulation is supposed to be a counterweight to the stress that the MC is put under by his companions, and that without her, the stress of being in a life or death situation broke the MC. Bury it under the 'flush toilet' jokes and the like all you want, but I think the MC suffered some real trauma there that's only being hinted at, and once he reached the apex of strength the first round he snapped, killed the party, and then killed the demon king. And then it was all reset and the special instructor let enough information slip to make the MC realize that this was all fake, completely delegitimizing the trauma he had gone through when Lanuvel died the first time, and the several years of suffering that followed.
And that's my second issue with the testing staff: they gloss over this potential problem entirely, which is strange given how the Special Instructor seems capable of sifting through past results of heroes to examine their actions and such. Think about it; if they had the ability to dig through data like they claim, they should be able to see a divergence between the MC and other hero candidates by Lanuvel's early death in the first round causing the MC to mentally break down into borderline personality disorder and PTSD, thus his current and recurring 'F' score in personality. It's the systems own fault for breaking someone who was a kid at that point and now mentally is what, 22? 23?
Note this isn't me hating on the series. I love it BECAUSE of this theme, this question about wtf is wrong with the MC. And its also why I totally empathize with the people who hate the MC; the MC does behave like a psychopath, he does things that are utterly grotesque, you're not supposed to like him, and it is very hard to feel sorry for him. Believe me, I GET IT. I don't like the MC that much either because he's a psychopath. What I love is the story, because I realize that what we're seeing is a high functioning psychopath being put through the world that gave him PTSD repeatedly, and a 'faculty' of testers, instructors, and graders who are unable to grasp the damage this kid suffered, and why he continues to confound their testing curriculum.
If this was the kid from before the first run, he wouldn't have had any problem acing the test. What makes his story special, why he's so different from all the other heroes that the system has produced, the diverging point about him is he suffered seeing Lanuvel's death early, the system was not designed to help the hero cope without Lanuvel, and because he grew up mentally carrying that trauma he is now incapable of understanding what the 'faculty' even WANT from him. The people aren't real, the 'good' decisions all turned to shit and caused civil wars and genocides if they were real, and they have driven the MC insane at this point, in a way that the faculty has no means or experience to draw upon as a response.
EDIT: Regarding the inevitable counterpoint of some of his internal narration, here's how I'll respond: what narration of the past we see happens AFTER his breaking point, and is a flashback through an unreliable (ie, insane) narrator rather than a live view of his state of mind at that moment, for example the death of Lanuvel what we see of the physical part of the flashback is the MC in clear anguish, and its not until the internal monologue about the event occurs that we see the 'jackass MC' emerge, the MC we know now. Essentially, my assertion is that he views some parts of his first adventure like the death of Lanuvel differently now than he actually did then because his brain is trying to simultaneously cope with the trauma he suffered on top of it being revealed that the 10 years of suffering did not matter, which colors his perception of the first run entirely. I'm going to stick with this point because as much as he yells at Lanuvel, he keeps coming up with more and more convoluted mental reasons to not do her any physical harm, and in fact often keeps her out of harms way subconsciously.
EDIT 2: borderline personality disorder, not dissociative personality disorder. derp.