Yeah. Even if they were genetically dispossessed to have higher IQs, better health and extreme motivation it should have been pretty genetically diluted after 600 years.
Assortative mating can help maintain or increase any endowment. Think of that as being a within-family/smaller-scale version of the existing genetic gradient by SES (eg "The Genetics of Success: How Single-Nucleotide Polymorphisms Associated With Educational Attainment Relate to Life-Course Development" https://www.gwern.net/docs/genetics/correlation/2016-belsky.... , Belsky et al 2016; "Genetic analysis of social-class mobility in five longitudinal studies" http://www.pnas.org/content/early/2018/07/03/1801238115 , Belsky et al 2018a.)