Teachers who provide feedback that doesn't make sense are bad teachers.
But, seriously it's so hard to judge whether an English teacher or not due to the tastes and preferences in English.
Some teachers expect a different structure to others (I've experienced this). Like, strict markers expect a different approach to an essay question to the more lenient markers. This becomes a problem when one teacher tells a class to do something then when someone else marks that class's essay, they receive low marks because the marker is not pleased with whatever the students did. While, the same marker who marks their own class's essay will be giving them the higher marks as they did the more 'right' thing in the marker's opinion.
Some teachers give you an unreliable grade on a prepared essay (pretend B+ or A) then when you go into the exam feeling confident, you get smashed (maybe, a C).
I, myself, know that my Advanced English teacher is bad while my EE1 teacher is good.
Then there's the problem where you wonder whether your English tutor is good or not.
That is the major problem of English. In Mathematics, Science, History and Social Science, etc. it's much easier to tell whether your teacher is good, average or bad.
I guess my post will be argued against but seriously, I hate the level of variability in English.
There will ALWAYS be a small level of bias and subjectivity in marking and teaching no matter how hard teachers try to be fair across the board.
We're humans after all.