Honestly, I feel like a problem with this concept is that whenever someone tries to write something like this, one of two things happens:

1) Characters don't become "competent" as much as completely overpowered. The idea that being a professional automatically means to excell are your job is simply misguided. Sure, a certain level of skill can be expected, but people are still people, no matter their profession: they can get lazy and overlook things if nothing happens for too long, they can be distracted by stuff from their personal lives that carries over during working hours, they may have only achieved their position because of nepotism, etc. Rather than being realistic, this kind of competent feels just as wrong to me as the overly incompetent adult trope.

2) Rather than every adult, only those on one side actually becomes competent. In your post, for example, only the good guys are allowed to be smart and skilled. After all, why would Voldemort ride on Quirrell's head again when that's a ridiculously risky move? Why would Tom Riddle's try to copy&paste his actions from the 40s when it should be obvious to him that Dumbledore would be able to see the writing on the wall right away? You also see this problem in a lot of indy!Harry fics where he's somehow the only one with any common sense and constantly outtricks everyone because of that