that is really disappointing. if you don't get any quest log update, no achievement, and no reward (if you kill HoD final) and even the shrine doesn't activate anything on your character's data, then why bother killing it. I for myself try to finish everything I can (perfectionist) , but if it changes nothing (and in this case it is absolutely nothing, not just no reward, that your character before and after killing him, has the same data on the server) there is no point :\
thanks for your answer though :)