what's wrong with 'go and kill stuff'? what else do you need? medals?
Not sure if you're serious, or just having a mirthless joke while agreeing about the utter absence of the career path and my expectations for anything beyond mindless pew-pew.
If it's the former... a military-career path is so much more than just "Go Kill Stuff". The current situation is a rep-grind, usually achieved by finding an edge-case system generating infinite donation missions to grind your way to max-rank, unlocking some permits and ships along the way.
FE2 had it nailed pretty well for it's time... while the initial options for low-rank missions were "Deliver blank access cards" with no risk, up to "Deliver intelligence reports" with low-level risk, they evolved into assassination missions against military target ships, and eventually bombing/surveillance missions which were unique to the military career path. There were "medals" which marked milestones in your progression which gave it a nice sense of pacing, but were ultimately meaningless, but it was something.
One of the cool things was that Imperial and Federal navy ships which interdicted you in the course of your missions actually employed unique tactics compared to your everyday pilots. Would be pretty cool if the navy ships in ED actually did that, as opposed to behaving just like any other pirate ship... but I digress slightly.
A massive issue right now with the BGS (and ultimately, the game) is the utter imbalance in favour of positive-state actions versus negative-state actions. Every other week there's a thread asking "How do I find famine/is the BGS broken because there's no famine?". BGS is fine, it's just negative-state actions are impossible to reliably conduct against factions compared to positive-state actions. Negative security states are slightly more present, though still grossly outnumbered by the prevalence of civil liberty. If you look closer... it's almost always anarchy factions in negative security states; a by-product of pirate lord assassination missions always targeting those factions, and causing -ve security.
A military career path would be the venue for undertaking missions or other activities which target negative effects based on superpower-affiliation of factions, which simply doesn't happen via any other mechanic in the game right now. Pursuit of that in favour of one side should promote and reward further activities against other sides, at the expense of interaction and security in the domain of that superpower (due to hostility, criminal records etc... this is also where the change to make notoriety Superpower-specific is important)