Why the CIO will struggle to become the Korean version of the FBI

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The FBI, as part of the U.S. Department of Justice, works in close cooperation with U.S. prosecutors.
As an institution nearly 100 years old (some consider its origins to be in the 1920s, so it may have already surpassed that), the FBI possesses investigative capabilities that are incomparable to the newly established CIO, which hasn't even completed its organizational setup.
The FBI members are not merely investigators; they are a public security agency that handles domestic counterintelligence and information security, similar to the NIS in our context.
The FBI Director is guaranteed a strong term of office, and the system ensures political neutrality to such an extent that even the President's involvement in principle would cause controversy. In contrast, the Minister of the Interior and Safety openly directs the investigations of the CIO.
An impressive remark by Prosecutor Park Sang-yong:
The reason why police in the U.S. cooperate so well with prosecutors is
that they face disadvantages if they fail to secure a guilty verdict at trial.
In short, it is a structure designed for accountable cooperation, and this is generally how English-speaking countries operate.