I'm not so sure if Starfleet models itself on real life military.
In my Head Canon, StarFleet offers you positions based on if that's what you want.
If you want to go the Admiralty Route, you can, if you want to be a StarFleet Captain for the rest of your life, you can!
If you just want to be the head of your department, you can!
Nobody forces you out of your position or "Force you Up or Out".
It's based on what goals you want to set for yourself and how you want to accomplish it.
If that means going Multi-Discipline and being good at it, then that is a viable option.
No Snobbery, No Elitism, No Pushiness.
The reason people want to be the "Captain" of a StarShip or StarBase is because of legendary stories of the previous "Great Captains"
If you want to be the greatest "Aviator" in all of StarFleet and fly the latest "Space Superiority" / "Atmospheric Superiority" / "Heavy Assault" fighter, then so be it. Or you can be a advanced "Shuttle Pilot". Whatever sticks to your fancy as an "Aviator". Or you can go and specialize as the pilot of a large StarShip and work your way up to the class of StarShip that you want to pilot.