I appreciate your response very much. I find the aforementioned subject more related to philosophy, mainly due to the person Richard Wagner was. Not only did he have a comprehensive worldview, perception of art and how it should be, of culture, of people, religion, politics and as we all know, "races" etc, but he actually wrote extensively about them. That's why I think the matter will require years and years of reading, researching and writing. The very fact of his writing extensively, sets him apart from other composers who would often be subject to study in a musicology department. Put aside the role he played, or they made him play in the Third Reich.
In regards with what you explained, about how music is studied within philosophy and aesthetics, can I deduce then that music-related topics other than this can be the subject of one's doctoral dissertation?