I'm running SQL Developer 17.2.0.188 build 188.1159 which does indeed contain data modeling capability. I just created a relational model diagram via the menu: File->Data Modeler->Import->Data Dictionary....
I also have the stand-alone Data Modeler, which does the same thing.
As the Data Modeler tutorial states:
Figure 4: Relational model and diagram for HR
The diagram you’ve generated is not an ERD. Logical models are higher abstractions. An ERD represents entities and their attributes and relations, whereas a relational or physical model represents tables, columns, and foreign keys."