If I'm correct, no one has died in the whole Aizen arc...
And probably in the whole show except Ichigo's mom and many bad guys.
For some reason I even suspect Ichigo's mom to be the captain promoted to the king's squad...
Nonetheless, all of these shinigamis seem extremely weak except maybe the commander, and five other guys including aizen. My point is that maybe this full scale battle is there to
train lower strength shinigamis and at the same time cleaning some demons...
My 2 cents
EDIT:
Well in the aizen arc, everyone from the concil (or whatever this chamber's name) has been killed...
But the idea remains. eventhough it would be an incredible stretch and incredibly slow development.