I would suggest introducing two things.

First, introduce The Diataxis framework ( https://diataxis.fr/ ) for documentation. It makes people think about documentation in a more structured way, and allows you to be more specific in the types of missing documentation. (High documentation cultures are often good with explanation but not tutorials, for example.)

Second, I would introduct the idea of a Documentation Portfolio. I have a review of Agile Documentation at https://www.ebiester.com/documentation/2020/06/02/agile-docu... and it speaks to another structure for how to build the documentation in a more reliable form and thinking more carefully about your audience for a particular type of documentation.