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...