Maybe its clever to make osiris more expensive?
Try to explain:
its cause extra damage (more than wrath banner) and its totally accurate!
Also it can be used against mages & penetrate magic armor as well.
Also, it fires throw all units in range, so sometimes it can kill artillery crew (at least 1-2) +some infantry and even other troops!
Can you make aimed shot with baner? No!
600-700 at least i think.