Would you be offended by this constructive criticism?

Your instructor is right. If I were you, I would even take some tutoring cles; on different writing styles. That way, you write with more confidence in your essays. That way, you know how to get your readers to comprehend what your talking about. I also would take your essay to an english professor. To see where your mistakes were made. I once had a history professor, tell me that writing history essays, are different than regular essays. I am still scratching my head on that. Good luck.