Metanarratives can be viewed as more and more explanatory. Basically, a postmodern view will consider a metanarrative better the greater its capacity to explain other metanarratives. The metanarrative that explains most is then considered the best.
But this is not the end of the issue, since there are lots of questions here. Some argue that no metanarrative will encompass all others and that no metanarrative is better than another in all contexts. And this is correct. If an individual is planning out their life and expect their life to be played out within a limited context, then they will generally approve of language that is hostile to the larger metanarratives. They may find people who use the metaphors of the larger metanarrative as "sinners" or "fallen" or "simply in error." So there are various ways metanarratives have of explaining what is wrong with people who use other metanarratives.
For postmodern people to impose the postmodern perspective on those holding a more limited view turns out to be contrary to the postmodern position! A view that recognizes the value of other peoples views cannot support a view that belittles or is insensitive to those other views.
The concern in our postmodern world is that very few individuals can grow up without becoming players in the language game of pluralism and relativity. The school system teaches teachers to guide students along a path of maturity. This path is usually interpreted in at least six stages.
Postmodern versions of these stages can be traced to Hegel, with Kierkegaard, Freud, Jung, Piaget, Kolberg, Gilligan and a whole host of others following suit. Aristotle described the nature of building character ("Ethica" is Greek for Character).