Having one-third legacy isn't really that strong evidence of a bias - legacy can be easily explained by (a) the fact that people who can choose between the top schools are likely to prefer Harvard for legacy reasons; and (b) the fact that academic success in general (and thus the ability to perform well in any school) is highly hereditary - all three of nature+nurture+socioeconomic status are strong influencers, and all are highly hereditary; so we should expect that a much higher proportion (compared to average) children of Harvard graduates have the innate qualities that would allow to choose among top schools even if there was no legacy bias.