Quartermasters are usually interacting with their respective department way more than HoPs do.
Quartermasters have 2 different roles as their underlings, making it fairly similar to CMOs and RDs command.
Additionally HoPs almost never act like they are heads of their respective department, acting more like pseudo-captains.
Here is what I wish the command structure would be, as it makes the most sense:
HoPs are bueraucrats that act way different ingame compared to what their role should be and QMs fill that void of local command.