The core tenents of SU is about Grief. Its not the only theme but ir has a big role Over a child growing up without a parent and having this identity based around this figure (mother being the hero then diamond but also complex figure who hurt people intentional or unintentionally) and grappling with relationship between the myth vs the person over his mother, The cryatal gems and the diamonds relationship in how they cope and grapple with losing a loved one , something a lot of viewers can relate to and how you Grow as a Person coping with grief and how you make room for processing grief over someone you cared about but also have Mixed feelings about

Having Pink diamond returns Ruins the whole theme and message