The reason we don’t see the cost allocated into different perspectives in the RDS cost report is that some assets may be associated to Aurora Clusters. The RDS cost report only categorizes RDS instances. This is by design.
The Cost History report resolves all the asset types but these specific asset-cost reports (like the RDS cost report) usually stick to one asset type, which in this case is AWS RDS Instances.
This means the asset type (Aurora Cluster) won’t be allocated into perspectives because the RDS cost report only resolves RDS instances.