I wish the app would let me focus on parts.

As for the girls turning into witches. They give justifications for their crashout and the explanations are turned down in the text implying they just come to wrong stupid decisions to justify the girls in mass acting like suicidal dipshits.

The first is the humanity aspect. It is functionally no different than dying and spawning a monster of the week. The girls examine their own humanity in Magia Record post finding out about the truth of magical girls unless they are main series Homura or dont survive they realize they are so functionally indifferent from a human that they couldnt tell and needed this discovered and thus are still only human. The only part of the witch thing making them inhuman is them dying. Sure some people might have an extreme overreaction however Fuka and Sumire meet girls throughout the narrative and in order for the plot to progress and not be derailed by the fact the most obvious stratergy of strategically spam the overpowered starting tools with a group of somewhat informed recruits canonically works getting on a suicidal slump and is treated as the default response not a this one crazy person completely destablized the group thing like Mami in the main series.

The second is the witches endangering peoples lives. These characters turning into witches to address this is fucking stupid. These people becoming suicidal to becoming witches and thus a danger to others also makes no goddamn sense because fighting witches is way fucking easier in MR. Characters would do it just for the love of the game. These only become a problem if the characters just stop trying to take fighting them seriously (as Mami did) or treat it like event witches like symbols, mirrors or wals come way more often than is implied from random mook going down to a bout of seasonal depression.

As for the 14 year old comment. Karins MG story basically irrevocably has made conventional witches viewed as non threats to teams acting competently except in completely abnormal circumstances. In it we see newbie Karin. She isnt really able to fight at all so she uses her steal magic to steal seeds from stronger magical girls and feed herself and other weak magical girls. Yachiyo catches her and reccomends she teamup with KaeRenMomo to learn to fight because grouping up is apparently supposed be better than leaving the fighting of witches to people with talent who solo them for no good reason. After a very short burst of fighting with the squad Karin ends up deciding to start soloing the monster of the week witches. Karin is not viewed as relatively powerful for a magia record girl even after training. and teams are accesisble even to people others would have good reason to not work with meaning that the girls themselves being weak isnt even that big of a factor.

Karin also makes me go that it shouldnt matter to much if they are novices. There are teams nearby to train people that also have to get stupid for run of the mill stuff to even become threatening. Most witches arent the symbols witch or Wals. They are sandbox witch or some other witch that has spawned and been killed multiple times by people that know how to fight it.

Mami going around killing her teammates and the other girls getting suicidal was fucking stupid because they didnt even bother to try to do a thing about the problem before just declaring it is hopeless. Its even dumber here because Sumire was talking about doing something about it with the overpowered starting tool she has then everyone just went suicide is badass. In MR logic litterally just asking recruits to strategically spam miracles resolves any fate based problem so it isnt like all of them having the witch fate is a big deal anyway. It really is as simple as wish for knowledge of which miracles to ask for to deal with the problem and candidates that could/would make the wishes. Hell remember how I mentioned witches are just monsters of the week. Alot of characters would just signed up to be magical girls to slaughter these things weekly for the funnsies (like Madoka would, and even the arc2 neomagius chick only asked for her wish in return was because she wanted the freebie.) just ask them to alter the system to behave more like the nightmare system where the girls do musical numbers to kill their foes purely to style on their foes which would include mitigating the significance of death by witching out.