I sense that there is a fundamental challenge in the question. The use of the mentor text concept is not entirely clear. I think that there has to be some type of clarification offered. Consider the definition of "mentor text" in trying to define the problem:
According to Dorfman and Cappelli, 'mentor texts are pieces of literature that we can return to again and again as we help our young writers learn how to do what they may not yet be able to do on their own.' Just as we learn how to walk and talk by observing and imitating others, we can help our students write well by using mentor texts.
The issue here is what skill or idea do we want to pull from Sophocles' work to find in our mentor texts? There has to be a specific notion or concept that comes is in Oedipus Rex that we want to find in another work. To consider it in another manner, there is something that is in Oedipus Rex that we might find challenging and need it displayed in other works to help make the concept clearer. Identify that concept or idea and mentor texts can be found. This works in reverse, as well. If there is something that Oedipus Rex demonstrates in a stellar manner, then it becomes the mentor text for us, in that there is something that Sophocles does which we would like to mirror in our own writing. I think that this becomes the central issue in the answering of the question. There must be a clearer distillation of what exactly is in the text towards which we seek to find mentor texts.