Original sentence: They do not make claims about the validity of their methodology or the certainty of the resulting conclusions.They use a combination of primary sources (original texts, but with archaeological evidence) and secondary sources (anthropological and historical studies)
Edited sentence: They do not make grandiose claims about their methodology or the certainty of the resulting conclusions.They use a balanced combination of primary sources (mostly original texts, but with some archaeological evidence) and secondary sources (the latest in anthropological and historical studies)