Allowing fully fledged mercenaries to kill overconfident children is just very counterproductive, and probably has something to do with the declining magic in that society.
I like Wirbel. He's cool.
Also the detail about how magic reflects the personality of the user is a nice detail to know. I'm looking forward to Fern and Frieren possibly developing personal spells.
Why the hate? This is an exam to become a FIRST CLASS MAGE. If there was no risk involved a lot more people would try to advance. The participants should be aware of these risks. Losing mages who are stupid enough to sign up despite not having the skill to fall back on is part of the exam. As most of the deaths were caused by monsters they would have died just the same if they were to take on a first/second class quest.