Would it be sensible at all to say Bro is the Dirk that didn’t know he was fucking up and didn’t bother trying to better himself when he did?

Dirk himself literally calls him that. “I could see how I could become someone like him if I were left unchecked.” It’s also likely Bro may have known his actions weren’t exactly the best, but when faced with solitude and the impending Death of Humanity, didn’t know any better than rigorous, insane training and bad parenting.