First of all, the professional level is high, not whether you have a diploma in this major (or whether you are a formal student in this major), but some students who are not in this major actually do not learn well, and some people have a high level. For example, Chen Qizhen is actually high flyers of the philosophy department, but he composes and sings himself, and some musical instruments are also played by himself. I'm an art major myself, but I've also made albums now (not to say how good I am) and I'm also teaching arrangement.
The second is that I can speak it myself, but I may not be able to speak it well so that students can understand it. For example, there is a swimming coach in the United States who can't swim himself, but even the Olympic champion has been trained. Moreover, some people have high talent, solid knowledge and good things, but it is really difficult for him to tell how to make them up. Art is a creative work without much skill and inherent knowledge, especially composition and arrangement, which is largely related to personal feelings, that is, inspiration and talent. A master musician said that composition can't be taught (only learned, there is no universal "teaching" in other disciplines).
I hope it helps!