We the People never gave government the authority to create or control the grand jury nor did we give Congress the authority to pass laws governing how the grand jury has to operate.
We the People created the Constitution, and in turn, created Article III which creates the Supreme Court. Moreover, within the Constitution, we allow Congress to create inferior federal courts. No State courts were ever created by the Constitution because the States were pre-existing Sovereign parties to the supreme law. In fact, it specifically States in article VI section II, which is the Supremacy Clause,
"... And the judges in every State shall be bound thereby,..."
The grand jury is solely mentioned in the 5th Amendment and nowhere else in the Constitution. It was never assigned to the government. As the late U.S. Supreme Court Justice Scalia once said,
"It is a constitutional fixture in its own right."
The grand jury is in fact our 4th branch of government and was designed to hold the other branches accountable when they failed to hold themselves accountable.
The grand jury was a group of people that investigated government corruption and misconduct without waiting for or being controlled by a prosecutor or a judge. They had unrestrained investigation and had an independent declaration of findings. Grand juries didn't need authorization from its constituting court to initiate an investigation nor did the prosecutor require leave of court to seek a grand jury indictment. It's swore in its own witnesses and deliberated in total secrecy so as to avoid intrusion from a judge and/or prosecutor. Furthermore, without the armed force of the militia, right alongside the grand jury, they cannot do their part to preserve, protect and defend the U.S. Constitution and maintain America's rule of law.
In 1946, the Federal Rules of Criminal Procedure were adopted. In rules 6 and 7, they denied future generations the traditional powers of common law grand juries. They inserted the practice of a prosecutor into the process. This prosecutor must approve and sign off on the grand jury's findings and that within itself is completely unconstitutional.