Hallo, bro, thanks for the comment, While it's true that I made him a student, it's only to make him interact with Rias, Sona, and others.
I could make him a teacher, but personally, I didn't like the student-teacher relationship.
About him being portrayed as weak, that was a writhing error on my part. Initially, I thought it was cool, but as the story goes on I can see its disadvantage. But don't worry, I will change that on future—when I get the right plot.
Anyway, thanks for the comment.