You are entirely correct, I fought the same fight at the Fires Center when I was in charge of the M777 and M119 programs from 2011 to 2014. It is not about what is the minimum number required to operate the system, but rather the manpower necessary to fight with the system. when you are operating any weapon system with 24 hours availability, the majority of the crew are performing other task. Realistically you can apply this even to a infantry Squad. Thanks to automation and weapons improvement, todays 9 man Squad is about 5 times more lethal and with more firepower than its equivalent 1985's 9 man squad. However, youcannot cut any additional person from the squad because it would become combat ineffective.