The laodshift theory doesn't work, the aircraft is loaded with mail trolleys, each bay is packed tight with trolleys that are strapped to the floor, then each compartment has a spider net close the compartment off
I do this kind of loading all the time and feel its much safer than carrying a bulk load of loose items or even containers, each trolley is a fairly light weight 80-110KG on average, if the load was not secure correctly im pretty sure some catastrophic would have happened on take off or in the climb
Just toadd that this loading is done with the FO as a supervisor instructing where to put each trolley so I would be very very surprised if it wasn't secured