i had something similar told to me, that the lead character is the one who the audience should identify and sympathize with. I was also told that determining the theme of story involves a math equation of how many times certain sentences are said relating to the theme. My teacher did like in Dead Poets Society and made an X-Y graph on the board of "theme intensity" versus number of times a theme is explicitly stated.

I tried like you did, saying that maybe a story's themes aren't always explicit or even internal to the text. I got a little intense and the teacher told me to sit down (i was an annoying teenager)