You know, I'm not sure about the plurals.

I would use that instead of which in the first - the hopelessness that he feels.

Would add a comma here - 'waste', 'abyss'
Can you use 'emotive language' rather than 'dark words'? ... create a sense of depression (or somethign like that), underlining the teacher’s view that there is no purpose to either his teaching or his students’ learning, while also characterising his view on teaching itself. (not sure the last part works tacked on there)

One example of this is the depiction of students as ‘unruly hounds’ (as described by the teacher in the original text) sitting at desks, straining against their leashes and scratching at the floor with their feet, their leashes held by the teacher as he sits at his desk.