Excactly what I think. Luke and Anakin Skywalker are related, but they are both strong and unique characters in their own right. In fact, I'm pretty sure them being related was something added in later, and not initially intended. The next main protagonist should be similar in this way. They should not ride on any other character's accomplishments or fame. If Luke had a clone son that resembles him in any way, that would defeat the purpose of making an entirely different character. I think having a student as a successor would make it easier for the next main protag to be unique.