The Hierophant receives the best possible armor and shields, supreme electric motors and shielding for maximum durability, and a beastly processor that enables a potent artificial personality with terrifying levels of intelligence and tactical expertise.
Hierophants are not intended to be used, and certainly not in war. They exist to carry out the most important tasks of the state, usually involving civil rights or the survival of the country.
Hierophants are top top secret, and when in public usually wear extensive ceremonial garb to hide their true appearance and capabilities. Unlike almost all our other battle droids, Hierophants do not have any connection to wireless networks and it is against their programming to communicate with any form of AI unless it is absolutely necessary to fulfill their mission.
The Hierophant operates on a totally unique operating system, and it's entire file structure is quadruple encrypted. Attempting to reprogram a Hierophant, assuming you could even get close enough to pry open the armored access port, would be an incredibly difficult task even for a super-intelligent computer let alone any human or alien programmer.
With superior intelligence, speed, strength, and durability the Hierophant is meant to protect the Republic from a machine-lead genocide against the organic and semi-organic parts of society. Although they do other jobs, their main task is to oversee the vast communities of AI and ensure they do not abuse their powers too badly. Hierophants are like robotic FBI agents for computers.