I have grown up watching mafia movies and reading everything I can about them, so I'm not some naive guy when it comes those kinds of movies but I was wondering

Did anyone else miss the fact that Sonny was the don? He doesn't do anything that makes him look anymore important as the Don he still just seems like a hot head who is "speaking when they should be listening" and when he was killed you didn't see the same emotion from the family as you did when Vito was shot.

So I was just wondering if anyone else missed that he was techinically the don/