I'm having trouble seeing how bro is supposed to be dirk other than them having similar interests. Bro seems like really oblivious to anything that has to do with caretaking but Dirk is smart enough to raise himself?

There’s a heavy, immense, utterly abysmal difference between raising yourself and raising someone else. Dirk knows his own limits, he likes rowdy training and strifing and is a man of combat, but he’s shown at every step of the way that he’s both 1) Absolutely and immensely socially awkward, and 2) Afraid that he’ll push his friends too far.

And that’s the thing, Bro’s rigorous training likely seems… Normal to himself. But for a 13 year old Kid, it’s a god damn hell. He literally sees it as nothing more than training to strengthen Dave, likely because he knows the End of the World is coming, and he’s dealing with the fact he’s put in care of one of the 4 Heroes that will have to do something about that.

Dirk himself says it, that he could see himself becoming that kind of person if gone unchecked. Think it more of how AR is rather than Dirk- A more immature, coarse and controlling personality. Besides, Dirk has the immensely positive influence of Alpha Dave, who he looks up to, while Bro doesn’t seem like he had anything of that sort.