I remember many years ago (like, 20 maybe) I took a serger class with a very famous teacher from a very famous company that published lots of books and patterns. I had (and still have, although a different brand) a low-end serger. She proceeded to make several disparaging remarks about my brand of serger, saying that it wouldn't be able to handle any of her fancy techniques and that it was a department store brand, blah blah, you get the picture. I was totally discouraged, but lo and behold, because I knew my OWN machine, I was able to make it do all of the things she said it wouldn't do. Even so, she pretty much ignored me the rest of the class, focusing on the people with the high-end fancy-dancy machines. When she did comment, it was to tell me that I must have gotten the ONLY serger of XYZ brand that was decent. Unbelievable! Totally turned me off her, and the entire company that she represented. I still think twice about buying anything they are sellling.
I guess the point is, as others have said, focus on your own machine, your own techniques, and don't let a teacher like that get you discouraged.