It depends on your business requirements. If the external source is unlikely to change and represents the data model you use in your app, you can map an Org-Data- child class directly to an external table.
Using the integration layer (Int-) gives you more isolation from the physical data source but also requires more rules to map into the logical data layer for the application (Data-).
The most important thing is that your business logic in your app references the Org-Data- class and does not reference the Org-Int- layer directly if you do choose to use the Int- layer.
If the requirement is to browse records from external table then do not need Org-Int class. But if we need to handle CRUD operations then better to maintain with Org-Int class where we can define RDB queries. Later map the response details on Org-Data class.