Imho, the service branches are defined by and structured around the type of equipment required to complete their missions.

The Navy builds years-long expensive ships, then sends them halfway around the world under command of someone. It has a structure to facilitate that.

The Army (at best) efficiency organizes a huge amount of people and material, and it deploys and sustains it wherever needed. It has a structure to facilitate that.

The Air Force procures, operates, and sustains the most technical platforms. So it's gotten halfway decent at doing that, or at least learned some lessons from repeated mistakes. It has a structure to facilitate that.

(And the Marines scrounge through everyone's trash bin, cobble something together, and come out armed to the teeth)

Point being, if you look at the people who have risen to the ranks of power, they've been moulded to fit their service culture. Which means some services might not be as good as procurement...