Anytime you use a dangerous weapon/instrument and cause any physical injury, it's an automatic Assault 2, doesn't have to be serious physical injury. Serious physical injury only applies by striking someone, etc.

You can't stab someone and get a DAT with assault 3 lol. But yes, as to your two drunks example, you could punch someone and only get charged with harassment.

Yes, nothing cops love more than high crime rates so they can get ordered in for overtime so they can't go home.