>A) there's ways around that stuff that any child can figure out.

No, there are not for hardware locked devices with the proper controls (what apps, websites, etc to allow).

>B) schools aren't in fact obligated to enable those, and some don't.

The technical problem is solved, if they don't want to implement the solution that's on them.

>C) who decides on what channels are allowed? The school does. But teachers are basically people off the street that did some basic training and (from my experience) have zero critical thinking. This are not the best and brightest.

Again, irrelevant. A common policy can be created (e.g. by ministry of education experts) and shared with schools.