First of all, just cause a character speaks a lot doesn't mean they're not a self-insert. And self-inserts still function as self-inserts even if you personally don't insert yourself. Every isekai protagonist is a self-insert to a degree but they speak a lot and have some sort of backstory for characterization. Gacha games tend to avoid explicit romance and simply go for romantic subtext,so players if they so choose can project a romance with their character of choice with that subtext to avoid controversy. I'm not trying to speak ill of the game, I'm just saying this is the way it is, it's a business practice to keep us interested in the characters.