If you believe the Joint Chiefs of Staff have any actual command and control of troops in the field, guess again.
While the Joint Chiefs certainly are the public face of the four branches of the armed forces that fall within the purview of the Secretary of Defense, they both collectively and individually can offer little more than advice to both the POTUS and the SecDef.
In fact, rumor has it that the Joint Chiefs only have three real functions;
Testify before Congress for a bigger slice of the defense budget pie Sign clothing regulations Attending cocktail parties
By the way, the various generals and admirals who’ve held those particular ranks are correctly referred to as simply general or admiral. There’s no such thing as a four-star general or a full admiral.
Anyhow, the real power lies in the various Unified Combatant Commands, better known as theater commanders.