The difference between a poorly performing product that uses an RDBMS backend and a highly performant one is purely down to SQL query tuning and finding the rig

The difference between a poorly performing product that uses an RDBMS backend and a highly performant one is purely down to SQL query tuning and finding the right indexes. It is the lowest hanging fruit to improve performance. Even if you don't have the flexibility to change the SQL on a project, you may still have the ability to create/rebuild the indexes to make the query faster.