After reading the updates, and the thoughts of others, I keep coming back to the same question:
Is this teacher actually TEACHING anything?
Or is she only teaching the C-level work?
From your updates, OP, it seems as though your DS is/was doing all of the B and A level work as self-study. And it was self-study to the point where it appeared that the teacher wasn't even familiar with the assignment or being very accommodating with the request (that whole salt thing still gets me).
So I guess that comes back to the question of why he has to spend his class time watching a video which has a questionable educational benefit, and then spend his weekend/off time doing required work that seems waaaaaaay above what one would think would be expected from a sixth grader.
Again, I would insist on knowing the impact that the videos play in the unit, and specifically how they will help any of the children attain their target grades. If the teacher is using that valuable class time for the videos, then I'd want to be shown why they are so beneficial. (Especially when I've just watched my kid spend countless extra hours of his free time doing work that could have been tackled in class but was displaced by the showing of these videos.)
And then if you can't get straight answers as to how these videos impact his grade, formally request that he be allowed to work in the library or somewhere else so he can use that class time to work on something that actually WILL impact his grade.