Yes. And if we can't grade great writers because it is subjective and we don't understand what makes a great writer, then we also can't grade good writers for the same reason. Or grade writing at all. We can say we like it, but that is subjective. Completely.

Now just for laughs, what grade does "Twas brillig and the slithy toves" deserve? Obviously an "F" because ole Lewis Carroll just could not spell.

Educational institution can and should teach punctuation. And spelling. But teaching writing? They get an "F" for that. And thinking? OMG don't even get me started!! :-)