It’s far more simple than that. The students are predominantly nobles, and they pretty much completely cut all ties to their previous lives.
So why would you send a hot daughter to become a witch when you can marry her and make political gains? You send the disfigured one so you don’t have to waste any more money on her.
The 5th son doesn’t need to be disfigured to be essentially useless in the political world.
Having everything in a single file is not really a problem.
Having extremely outdated info on topics like below is a major issue though.
Huh?