The problem with this type of thinking is that it undervalues the role that non-vital communication has in social species. Look at uncontacted peoples around the world. They've had music and dance even though their tribes consisted of a couple hundred people. These forms of communication serve a role in their communities but it isn't "there are fish in the pond over there" it's more special and abstract.
If we are to treat whalesong the same way then we can't immediately assume that they're just trying to communicate base concepts.