Military rank is more than just who salutes whom. Military rank is a badge of leadership. Responsibility for personnel, equipment and mission grows with each advancement.
Do not confuse rank with paygrades, such as E-1, W-2 and O-5. Paygrades are administrative classifications used primarily to standardize compensation across the military services. The "E" in E-1 stands for "enlisted" while the "1" indicates the paygrade for that position. The other pay categories are "W" for warrant officers and "O" for commissioned officers. Some enlisted paygrades have two ranks.
The Army, for example, has the ranks of corporal and specialist at the paygrade of E-4. A corporal is expected to fill a leadership role and has a higher rank than a specialist, even though both receive E-4 pay. In the Marine Corps, a master gunnery sergeant and a sergeant major are both E-9s, but the sergeant major has the higher rank.