I feel like I can answer this question simply with another question.
How would Bobby have raised Sam and Dean?
Bobby might have been rough around the edges and a functional alcoholic, but he loved those boys. And whatever argument you make to excuse John’s behavior, Bobby was put through worse. John’s dad disappeared when he was a kid? Bobby’s dad beat him and his mom. John saw his wife murdered by a demon? Bobby was forced to kill his wife himself when she was possessed by a demon. But he didn’t throw his life away for the sake of vengeance, and he took care of those kids better than John ever did when the bastard dumped them on Bobby’s doorstep.
See, teaching them to be hunters doesn’t equal isolating them from friends and family and depriving them of any sort of stability or home. It doesn’t mean leaving them alone in shitty motel rooms eating shitty food over fucking Christmas while you chase down cases no one is forcing you to take. It doesn’t mean turning them into child soldiers whom you don’t actually teach or confide in but use to your convenience and give only as much knowledge as you see fit. It doesn’t mean brainwashing your oldest child into believing that his only usefulness is to look after his brother, putting responsibilities on a child that would be unreasonable for an adult, and it sure as fuck doesn’t mean verbally and emotionally abusing your children at every opportunity.
It also doesn’t mean abandoning them without any word of where you’ve gone or why, and literally refusing to speak to them when they are desperately trying to contact you. Cause, you know, one of your son’s girlfriend was murdered and your other son is dying of heart failure.
Bobby would have taught Sam and Dean all of the lore in his library. He would have taken them out back and taught them to shoot, taught them hand to hand, and then he would have played catch with them, made sure they’d done their homework, ordered them pizza and tucked them into bed. He would have operated as a hunter from his home base, and he would have gotten choked up at Dean’s high school graduation and thrown his arms around Sam when he got his acceptance letter to Stanford.
Bobby would have been gruff and had a hard time saying ‘I love you’, probably wouldn’t have ever just come out and say it like that. But he would have been proud of his boys, would have said ‘good job, son’ and ‘atta boy’ when they hit the center of the target AND when they got straight As. He would have given them a home, a place to put down roots, even if it was a little shabby and messy. He would have sat with them at the dinner table and listened to them talk about what they’re dealing with. He would have made sure Dean didn’t take all the responsibility for Sam onto his own shoulders.
Bobby would have been their dad. He would have been there and he would have taken care of them and loved them.
We saw a perfect example of that with “Dead Man’s Blood” — John doesn’t tell D&S what signs he saw on the road to let them know they were going in the right direction until Sam pushes back and makes him. If that’s a good sample of how they used to work together (and we certainly get the implication it is), him giving unexplained orders and expecting them to shut up and obey, then he was a terrible teacher.