The sole and total purpose of iriminage is to break an attacker's neck.
That's funny, the purpose behind my technique seems to change frequently depending on what i'm doing.
There is a version of irimi nage that breaks the neck. I've seen another version that's supposed to be a stab to the chest with a tanto. Another one where you grab their hair or their gi and pull them down. Another one that's a cut up into the face with a katana. Another that's a whack on the nose with a jo.
Though we may generalize a motion with words like iriminage and shihonage, when a technique is done DIFFERENTLY it becomes a DIFFERENT TECHNIQUE.
Your shihonage may bring their arm off to an attackers side and break it. Mine brings the arm behind the back and pulls them to the ground. Though we both call it "shihonage", the technique and intent and purpose behind it is different. Do not be so quick to say that x technique has a sole purpose. The purpose may not even be to defend yourself or to even bring an attacker down. (what if my technique's purpose is to give uke a good back stretch?