Yeah, RDBMSs do have some big advantages; one of them being the plethora of query patterns possible.
If there are other parts of your application which are consuming the same data but in different patterns, it might not be necessary that systems like DynamoDB work in those cases. You might need to make several secondary indexes in those cases and all of them require provisioning of their own. The other alternative being setting up some ETL layer which transforms the data and sends to appropriate sinks, from where they can be consumed; but for small services that adds more moving parts and cost to the system.