I know very little about databases, but I work heavily with category theory, so fwiw: I think the main benefit is composition. The edge over SQL shows up when you combine schema mappings - a mapping is a functor, so when you migrate data along it the constraints come with it by construction, and you don't end up writing ETL and hoping integrity held.

As best as I can tell (but i really dont know much about databases) it's probably a narrow advantage - storage and everyday queries still go to Codd's model - but for stitching schemas together it seems like it could work.

I'm using similar math for automated formal verification, where this approach is what makes it tractable.

I haven't used CQL but this is how the advantages have been described to me as well.