A "high write volume" requires fast disks, and billions of rows require large disks. Two simple requirements that are the same for any relational or less relational database.
What's interesting is query performance, and a RDBMS supports explicit control over indexing (usually including analyzing execution plans to find out which queries are going to work well). Where do you see "a terrible waste of engineering effort"?
What's interesting is query performance, and a RDBMS supports explicit control over indexing (usually including analyzing execution plans to find out which queries are going to work well). Where do you see "a terrible waste of engineering effort"?