Are all the angelics organized into a hierarchy?

This is the case. And the example of archangels having their legions of helpers is an example. This allows them to take on very large-scale projects that may require many divine helpers to execute. This is true frequently during times of calamity, whether a natural disaster or an act of war or some other scene of tragedy where there are mass casualties. During such events, there is a great need simultaneously for many to receive support and healing. So this system provides a logical way to organize the troops, so to speak, and manage things with high effectiveness because all will be working in concert and know their roles. All the angelics are highly experienced and are very, very effective in all they do.