He was supposed to be a good kid who was saved by Sonny from an abusive alcoholic father. It explains his intense loyalty to Sonny and his anger after Sonny got killed.
Tom’s anger after Sonny got killed? I missed that. He gets choked up when he tells the Godfather.
His loyalty wasn’t in doubt. Sonny found him on the street and he was unofficially adopted by the Corleone’s and lived with them. His character wasn’t congruent with that IMO, that he was raised in that house as one of them. Maybe more of his back story would have helped.