If what you say is true, the problem seems easily fixable -- makes children of alumni enter through the normal channels, and not mention their parents, and if they will get in if they deserve to.
https://slate.com/business/2019/09/harvard-admissions-affirm...
Only some schools take into account legacy status, so wouldn't it be possible to do comparisons between schools that do and schools that do not to get those kind of stats? Many students apply to the same school their parents went to even if being the child of alumni does not give them a boost.
Of the top 10 universities in the world, according to US News & World Reports 2018 list, 4 take into account legacy status (Harvard, Princeton, Columbia, and Stanford) [1].
6 do not (MIT, UC Berkeley, Oxford, Caltech, Cambridge, University of Washington).
[1] https://www.cnbc.com/2019/03/16/top-universities-that-do-not...
"Our model of admissions shows that roughly three quarters of white ALDC admits would have been rejected if they had been treated as white non-ALDCs."
The barrier to entry for a lot of people isn't even being good/smart enough -- it's being familiar with or having the resources to navigate the bureaucracy that obfuscates the opportunities which are ostensibly open to "everyone".