I tend to think of dataframes (R, Python pandas) as the standard way for representing and working with the data contained in a .csv. “List columns” (https://jennybc.github.io/purrr-tutorial/ls13_list-columns.h...) inside dataframes can actually be a convenient way to represent data that is mostly flat, but has some hierarchical data associates it (recent example: dataframe representing a corpus of documents, with a column containing a list of citations). So while .csv probably isn’t the best format to store hierarchical data, it’s fairly trivial to work with if encountered.