Could this client-communication dashboard be built without Airtable, e.g. using Google Drive or OneDrive for client documents?

The response was that it's probably possible, but Airtable is preferred because it functions as a true relational database, and the app builder used for the internal dashboard runs off of a database rather than a folder or file structure. Pulling from a folder or file was considered possible, but a true database was described as running "a little bit better."