I agree with musclewizard, and Macharias, Plushy. Maybe these archetypes shouldn't be named after ranks or designations. Maybe they should have just named the sergeant "Hero", because he's a guy everyone gathers towards, and looks up to. Maybe they should have named the heavy gunner "Brawn", because he's basically the same rank as the weapon specialist (which is actually a rank, "Specialist", above privates), only bigger so he has to lug around the bigger weapons, and also he has a bit more HP. The operator is fine, because he's basically a private that's trained to drive (operate) a tank (after the appropriate training). The weapon specialist…why not just call him a Gun Enthusiast, or just Infantry, or something? He seems to be a mashing of whoever is "none of the above / Generic Guy" and also "the guy with special weapons in the table top game". And Medic? What a specific role. Can I be a mess cook as a role as well? How about the guy who drives a forklift at the warehouse? Maybe just rename him to "Brains" and he can be more proficient at more support roles (like using a typewriter).
By removing these rank numbers, you can now follow a "Brawn" from boot camp, to trenches, to becoming a veteran, to eventually becoming a leader as a sergeant. Who knows, maybe he'll be lucky enough to go to Officer School, and become a luetenant. I'm not saying everyone get's to be an officer, but I am saying there should be a feasable system for some to become an officer.
EDIT - I'm not trying to be a troll. I'm just saying, this is the perspective some potential audience might approach this ruleset. For me, these are hurdles that would make it really hard for me to get into this game. Nomenclature is important, especially in a large organization, where everyone needs to be on the same page.