If you observe and think about it, the four heroes summoned, for better or for worse are all humans.
There is no perfect human.
I don’t know the criteria used for the selection……But, thinking about it, there are certainly some heroic dispositions.
Take Motoyasu for example; he is a feminist who is incredibly fond of women. Thinking back, when he heard about Raphtalia being a slave, he took the righteous action to release her, although from my standpoint he was just an annoying guy.
Ren wanted to go save the village that was in trouble.
Even Itsuki, though he’s a little inconsiderate, I think that his attitude on not allowing bad things to happen is to some extent, Hero-like.