Diversed as in well defined, written and, partially, animated the characters are. It has much less to do with the "first impression" like you are suggesting, as in being a party of males or females, young adults or grown-ups... Etc
From gameplay perspective as well. A party of one does not equall having limited playing style in games in general not just RPGs ( look at infamous second son). It is up to the vision that the gameplay was based on.