Yes of course, the publication of a theory of just war will prevent things like Iraq, Afghanistan, Libya, Syria, not to mention the genocides in Rwanda and the Balkans.  As soon as it is published, we can expect the 1.2 billion catholics to rise up and force its application.  No, this is just an academic exercise that will produce no change.  The people who wage war will do so on their own terms with their own justifications, as they always have.  
You miss the point about the contrast.  Whereas the church does not have a military and cannot stop war, it does have bishops protecting pedophiles and it can stop that.  The church has one commission busy generating a nice little document that won't change anything, while another commission does nothing even though it could change an injustice.  One might conclude Francis is more concerned about appearances than making a real difference.