Millions of read-only historical transaction records are a large-data-volume archival pattern, not a normal transactional custom-object pattern. Big Objects are designed to store and manage massive amounts of data on the Salesforce platform, especially historical or archive-style datasets. External Objects are also valid when the data remains in an external system and Salesforce needs to surface it without fully storing it in core object storage. A standard custom object may create storage, indexing, and performance problems at this scale unless heavily architected. A long text field is completely inappropriate because it destroys record structure, filtering, indexing, and security granularity. Avoiding storage does not meet the requirement to display the records. The FlexCard can display the summarized data, but the underlying object strategy must support high-volume access.