I'm late for the party, but I agree with everyone, everything up to this point had been a rather fun if a bit too trophy travel, just fun "junk food" isekai, but the choices made in this chapter are questionable at best. As others have pointed out, he showed he is strong enough to defeat everyone, even when confronted by the headmaster, the MC gave up because it would be too much of a bother, not because he felt the headmaster was stronger than him. At the very least, the headmaster could have been more smart in his approach, like saying that he wouldn't disqualify him and the two girl friends if he refused to be labelled as the worse, and since the MC knows how important is for the first girlfriend, he would agreed to it. It would make the villain headmaster look more cunning, and the MC more selfless. But as it is, it just look like a paint by the trope manga. I will continue reading, but I lost the wind that I had until now.