your tl;dr is a bit strange.
it's easy to look at gaokao, NEET, and CSAT (called seuneung), and gawk at how difficult the exams are, because of how the media and society represents migrant students. comparing gaokao, neet and csat to maths extension 2, is actually far more similar then different.
Consider these JEE past questions:
JEE Main Mathematics's Sets and Relations, Logarithm, Quadratic Equation and Inequalities, Sequences and Series, Mathematical Induction, Binomial Theorem, Matrices and Determinants, Permutations and Combinations, Probability, Vector Algebra, 3D Geometry, Complex Numbers, Statistics, Mathematical...
questions.examside.com
Consider the CSAT past question (this is the hardest question in the exam):
While these questions are definitely harder than then HSC papers we've gotten so far, it definitely isn't a moonshot compared to some NSB and James Ruse questions we've seen. I'll remind people that not every takes the CSAT in Korea - especially the hard version everyone thinks about. There are different lines students can take, and the hard maths variant is generally taken by engineering/STEM students.
So:
1. What we learn is incredibly similar (between MX2, and CSAT, JEE etc.) (CSAT english is called difficult, but really... what the HSC asks of us to do is far more difficult; CSAT is multiple choice, as well as Korean being mostly multiple choice and short answer).
2. We shouldn't glamorise these countries testing schemes, because they have the highest student suicide rates in the world. We should strive to be a country which is successful.
3. We shouldn't be reaching to the standards of these countries, because even though their exams are 'so much harder', our top universities are very similar in ranking. (UNSW, USYD, ANU compared to Seoul National University).
What benefit do we have from over-exerting our high school students? We're 18, and to define our entire lives (which many of these foreign countries do), on a high school exam, is beyond idiotic.