As someone with 20 years active and reserve time, the only thing I'd really tweak here is that the budget is somewhat centralized; it's just the execution that's decentralized. DOD is an Executive Branch department that operates on money programmed by Congress. Agencies choose, within limits of Title 10 US Code, how to spend that money, but the "pots" or "flavors" of money they have to spend are allocated in the Congressional budget.