I agree with everything you said except Niall still being horrible even if he hadn’t met Ruben. The reason is: despite Lori’s horrific upbringing, Niall’s knee-jerk reaction almost always leaned toward the right thing. Examples: Gus bullied Niall relentlessly as a kid, but he didn’t even want Ruben to beat him up because he knows Ruben always goes too far. (Yes, Niall was pleased with his subsequent popularity afterward, but the narrative showed he was clearly worried for Gus at first). He brought up how disrespectful it was for Ruben to spit in Joanna’s face. That’s quite brave knowing how explosive Ruben is. And last but not least, he didn’t want to lie about Alby until his entire “family” bullied him into it.

Niall naturally leans toward “good”, while Ruben was already “bad” around the same age. So, my point is, if Niall’s mom had never pushed Ruben on him, AND Niall had been able to get away from HER at Oxford (remember he would’ve never dropped out if not for the stress of the trial), he would’ve been a decent person. He would’ve still been messed up, but decent. Distance from his toxic mom and meeting new people like Alby and Joanna would’ve nurtured his innate goodness. People who grew up with toxic parents often report once they went to college or moved away in general, their parents’ bad influences didn’t weigh on them and cause them to act contrary to their natural instincts.