I don't think that's the point of legacy admissions. I think it's purpose is exactly what the grandparent said which is to cultivate a network of people.

The problem with saying legacy preference is to take the place of higher performing non-legacy candidates is that legacy admits generally perform above average at least at Harvard although it's probably true elsewhere. See here[1]: The average SAT score among legacy students was 1543, while it was 1515 for non-legacy students.

So it could still be for replacing higher performing non-legacies meaning Harvard targeted and rejected a bunch of people with even higher SAT scores than the legacies but I don't find that very convincing.

[1] (https://features.thecrimson.com/2023/freshman-survey/academi...)