What I mean by that is that the author makes a big deal about the MC having gone to USA and worked as a prosecutor there for X years before returning to South Korea to become a star prosecturo in South Korea since having worked X years in USA = being a top prosecutor in SK.

Now while it is true that being a prosecutor in another country would give you a lot of experience you also have to keep in mind that different countries have a lot of different laws and outcomes in their cases so just that holds a big difference from country to country. But the major thing is that in the world there are two major legal systems called Civil Law and Common Law which to a fairly large degree differs how laws are applied and interpreted. Civil law is by far the largest of the two and is mostly formed by codified legislations and legal rules while common law is mostly based of precedents and court decisions. In short Civil law is mostly centered around what the law says and what the prepatory works say about the laws and how they are to be applied and interpreted. While Common law on the other hand focuses more on the outcome in a similar case that has previously been ruled, even if that was hundreds of years ago and the law hasn't changed much.

While both systems refers to and applies old cases to new cases Civil Law has a much larger flexibility but also makes it harder to know the outcome in a particular case while Common law is often times less flexible with sometimes more predictable outcomes which also makes it often times faster and easier for the court system to work.

Getting back on track however, as mentioned Civil Law is what most of the world runs by and is the system SK uses and USA on the other hand uses Common Law which is the system the UK and it's british empire ran by, so most countries that were a british colony at one point or another uses Common Law. So the MC has been using and working with the Common Law practice for years and then moves to a Civil Law country and just instantly becomes a genius prosecutor. Honestly it would have made much more sense to have the MC work as a prosecutor in any other country with a Civil Law system instead.