Now you know what not to major in. If you ace everything you'll never know if you made the right decision. Grading on that sort of thing is completely subjective, he lowers your grade because you don't see it his way or agree with his view. I'm betting there's some high power profs that would disagree with him too. They never all agree on anything.
If you did your best, fuck it. If you didn't, do so in the future, lesson learned. That's way more important than any poem...or poet. I'd take your ass over a poem any day.