What would the relational diagram look like in this situation?
I am with your teacher here. I cannot see any difference in degree of Normalization between the two solutions, but you are embedding aspects of a particular implementation presentation (Two views of what is often referred to as the External or Logical Schema.) into the core data structures. When performing the initial database design (of the Conceptual Schema) it is preferred to hide as much as possible both of the external presentations and of the physical table design.

Once the Conceptual Schema has been designed (and fully normalized), then one would determine the best way to present the Logical views of that structure to external applications, and the optimal physical assignment of columns to tables (the Physical Schema) to maximize performance.

Your proposal is pushing subtle choices of Physical and External design into the Conceptual Schema inappropriately. 

It appears to me that your teacher is having difficulty explaining that your proposal might be a valid physical database design, later, given certain assumptions, and accurately reflects the External views as currently implemented, but fails to meet the needs of a Conceptual Schema that maximizes normalization with minimal clutter.

A key observations is that whenever two tables (entities) have the same Primary Key, then even if the normalization is the same the clutter has been increased. There will always be many ways to clutter a clean (Conceptual Schema) design, but this clutter can always be eliminated from it. In a real world database design with hundreds or even thousands of tables minimizing clutter is an essential design attribute.