Did the criminal justice system really have to be torn apart like this?

The prosecution has been torn into pieces—split into the Prosecution Service, the Serious Crime Investigation Agency, and the Corruption Investigation Office for High-ranking Officials—and even their authority for supplementary investigations has been stripped away. A system that once functioned as a single unit has been fragmented into multiple parts.
For example, if you fall victim to investment fraud, 500 million won is now the dividing line. If it is over 500 million won, it goes to the Serious Crime Investigation Agency; if it is less, it goes to the police. If the damage amount is ambiguous or involves multiple cases, the victim first has to figure out which agency to approach.
The bigger problem comes after that. Even if the prosecution side determines that there is insufficient evidence, they no longer have the authority to supplement it directly. A matter that could be resolved with a single bank account trace now requires the entire case to be sent back, and in the meantime, criminals embezzle funds and destroy evidence.
One might think that splitting agencies would increase expertise, but in reality, they simply pass the buck, claiming a case is outside their jurisdiction. By focusing solely on weakening specific agencies, they have completely broken the system's ability to provide relief to victims.