Great question, no pun intended. This is an important question for the OP, who proclaims (in all caps) —

WE ALREADY HAVE A GREAT LEGAL SYSTEM, BUILT OVER CENTURIES. At least in the United States and other highly developed parts of the world, that is.

There are no robust objective metrics for “greatness” in this context. Any proxy for that benchmark, like, say, the World Bank’s Doing Business Reports, or AI/HRW rankings of rights, etc., are open to many lines of critique — of a methodological & substantive/theoretical nature.

Which is why it’s best to avoid crude subjective nativist badges like these. Too slippery a slope.