I do not how you can saw it was self-aggrandizing.
The dramaturg noted that all sorts of theatrical staff (including the playwright themself) act as dramaturgs. He does not make great claims for what he does and does not claim responsibility for the script. Rather he notes what his job duties are in an especially clear way.
Even if there are no official dramaturgs, most writers have trusted advisors, friends, etc who read the play as it is being created. Writing never happens in a vacuum.