I dont think there are only 9, when a group is so important and small Oda usually have the number stated out loud or as part of the name(4 emperors, 7 warlords, flying 6, etc) but thats not the case here. I think the silhouettes are just a generalization of an actual army, wich will be mostly of composed of powerful fodder(but still fodder nonethess) and a couple of strong guys to fight the Rev captains and vice captains. I still belive in Robin's words that the admirals are the ultimate weapons the WG has when it comes to fighters, and that only Imu has the potential of being above them