I hope he finds a good role model and develops a more healthy approach to life.

I do as well. He needs to escape the shadow he is letting himself live under and look out into the real world. Which is hard when you live with that kind of mother as he describes her, but life dealt him a hard hand. Its either play or fold, no matter how injust that is.

My assumption is he learned the unhealthy tactic of complaining online from watching his parents

He has been streaming for at least a few years now. Meaning he is already learning those unhealthy parasocial behaviors that even adult streamers fall into. Which should probably be the first change he makes, to both help himself and sever his father's shadow.

My belief is that a parent must try to shield their children from their parents' mistakes as much as possible, while still teaching the children how to avoid making those mistakes.

Agree entirely. Unfortunately it seems in this case the egotistical Destiny's influence is to make him a complete copy of him. Which is awful on many levels.