As a reference: The Chinese equivalent, Gaokao [0], is notorious for its brutal difficulty, but also widely regarded [citation needed] as a great equalizer. To that end, high school students spend obscene amount of their class time doing test prep (yes, in school instead of after). Although YMMV, and the total score usually spreads out quite nicely without need for curving (one such attempt was recently made [1]; it didn't turn out well). That is, despite all the extensive test prep, Gaokao simply refuses to be maxxed out (effectively, due to human scoring of essays). With all its problems and totally valid criticism, Gaokao remains (IMHO) the golden standard in equality of opportunity. Sadly China is moving to "diversify" college admission recently --- euphemism for bias towards wealthier families.
That, however, does NOT favor the rich, mod cheating/forgery, which surprisingly does get caught, due to the widespread expectation of the system to be fair.
And there used to be bonus points for STEM Olympiads, which had totally worked as intended by providing a sound alternative for the talented / hard-working specialists who have not so much family backing. There were varying degrees of cheating (mostly in the form of leaked problem banks), more rampant in some provinces than others, but AFAIK the asking price was not totally out of reach for the common working family, so it'd be unfair to say cheating the exam favors the rich either.
I don't think it's true that the Gaokao is regarded as a great equalizer. You might be misled by the fact that it is regarded as the only potential path out of rural poverty in China - but even in the wikipedia article you link it discusses many of the issues with it. And this (2014) NYT opinion piece covers some in more detail (including that yes, richer students also spend time after school preparing). https://www.nytimes.com/2014/09/05/opinion/sunday/chinas-edu...
[0]: https://en.wikipedia.org/wiki/The_National_College_Entrance_...
[1]: (Chinese Wikipedia) https://zh.wikipedia.org/wiki/2018%E5%B9%B411%E6%9C%88%E6%B5...