I think the main problem with this kind of story is that every time, a new villain is introduced as OP and the top of their field (here, the headmaster was a war hero and whatnot, and the new guy seems to be a genius of some kind that was able to repel one of the OP characters easily), all that to discover once they are defeated that there is something above we didn't know about, and the defeated villain was actually trash.
It works a few times, but as the pattern repeats over and over, the meaning of power just gets lost, and the story becomes dull.
I think, fundamentally, you and I look at this series differently. You're looking at this series like a naruto/bleach type of series, where the protagonist will(/needs to) be scaling up to meet the difficulties of a new enemy, whereas I see this series as more of a violet evergarden, where the real story is about how the protagonist interacts with side characters, and how he changes their life (and in the first place we might've had how it affected his own life/story, but I don't think he's self-reflecting so much anymore).
I don't think this newest development should be that much of a shock. The special-class knights are considered a tier unto themselves, much as s-tier adventurers are, and that was set up way back in like chapter 2. Honestly I feel like Alicet was kind of just playing around, because her personality is just to be playing around and shout boom and fire off a magic spell that most people would be overwhelmed by.
Also, last thought, I think the story does kind of set up that Klein isn't all that remarkable. I mean, I won't say it's not rushed, but we learn that even though he's a knight of the round table, he's put on a ton of weight, and nowadays people don't recognize him because it's been 20 years since he earned a name for himself. And we also know that he's taken on the duty of an academy headmaster (to me it implies he's not doing knightly duties other than that, but that's definitely just my assumption).
lol, sorry if I'm doing too much to try to defend the series, in my defense, I have spent a few hours with her