By diversity in psychology, I'm referring to the many diverse subdisciplines in the field, not cultural diversity. Why should it be considered a strength or a challenge?

          Diversity in the field of psychology can be considered a strength and a challenge. Having diverse subdisciplines in the field of psychology allows students to gain critical knowledge, abilities, and skills in regard to having a successful career in psychology. That is, being beneficial in regard to assessing, testing, and treating clients. As well as in regard to performing research and teaching, and such knowledge, skills and abilities can be very impressive and desirable for potential employers (Landrum & Davis, 2010). Also, diverse subdisciplines give individuals or students ample careers opportunities, that is, in regard to a diverse choice of subdisciplines to concentrate on or more than one subdisciplines to concentrate on. However, learning from and about diverse subdisciplines can be a challenge. There is an enormous amount of knowledge to gain and retain.  

Reference

Landrum, E., & Davis, S. F. (2010). The Psychology Major: Career Options and Strategies For Success (4 ed.). Pearson Education.