I have a feeling Tatsuya is actually far superior in magical skills than everyone around that school, and the president seems to think the same.
It's like if he's in a kind of undercover mission where he needs to be a weed so that he flys under everyone's radar and or he gets some contacts he could not get with an elite undercover. It might also be that megane girl is in a similar situation for another party.

Regarding the brocon, my guess is that we'll learn Tatsuya ins't her blod relative.
I usually do not like the brocon theme, but for some reason it felt genuine/strong and deep and left me with wanting to know more.

I hope to be kept untentained with that show.