I've heard people complain about P5 social links being called confidants and justifying themselves by calling the change unnecessary and (correctly) stating that the word confidant has a less friendly connotation than social link, but I think they just miss the point entirely.

Changing the term to confidant isn't just "to be edgy" or to fit in the motifs of the game (although it does both of those things), it's an important bit of characterization for the protag, a character that severely lacks such details in an effort to make him more relatable.

P5 has strong themes of social isolation throughout, manifesting itself in character traits of all Phantom Thieves, and the MC is no stranger to it. His classmates constantly reject him throughout the entire game, and treat him as if he doesn't belong.

It shouldn't be a surprise, then, that he views social interactions as purely transactional; I'll do this for you if you do that for me. When he maxes out a bond with another character, the game remarks that they share the same goal and have reached an understanding.

The term confidant not only fits into the themes of the game, but sheds light on Joker's inability to connect to others around him on a personal level. To say it's due to mental illness is a bit of a stretch, but it's a fine detail that makes a big difference contextually.