His argument is that if I have two 45 bay chassis with 8TB drives. If the a chassis were to fail that's less data loss than if they were a single chassis with 16TB drives.
We'd repair the server in either case but he wants less risk.
It's solely dependant on how much data is in one location.
However we are now moving datacenter were space is now a premium and so is energy usage as we are over capacity for heat and power at our current location.
So price and data density are now more important than a programmer's feelings.