Is there a use case where RDBMS is the best data store for querying only?
I find your question a bit confusing, as you mix different concept domains togeter.

RDBMS stands for "Relational database management system". If your data model is relational in nature, you use an RDBMS to store, process and query it. How it optimizes these things physically is an implementation detail (your "Column Data store" is one example).

If your data model is strictly non-relational, you might choose a different DBMS, such as key-value store type, whose implementation is more optimized for the corresponding use cases.