Is Kim Kardashian’s star power fading, even as her multibillion-dollar brand Skims continues to grow?

First there was Princess Diana, then there was Kim Kardashian. Both women dominated the aesthetic of an era, and their faces and bodies were constantly splashed across newspaper front pages and in glossy magazines. Their love lives, children and mental health were dissected in forensic detail, and the power of their brands mixed with the adulation of their fans meant that almost anything they touched turned to gold. But whereas Diana’s tragic and untimely death held her star power in amber, Kim...