i'm with unsung, INTJ, 5w6 or 6w5, sp-first. seeming not to have compassion but then standing up to bullies is probably hidden Fi - maybe INTP / inf Fe.
does he seem unhappy, overall? he has expressed boredom. no specific interests but he likes to debate? that sounds like an interest. can you find a local debate team, maybe? local chess competitions. more things to engage his mind. if he's INTx 5/6 like it sounds, he probably finds a lot of normal stuff boring and stupid. my little brother is INTP 5 and is like that. oh hey, what about music? that's a really intellectual thing, and music calmed him as a child. a soft, gentle instrument like piano or acoustic guitar could be engaging.