The rise of personalized and algorithmically curated media environments has transformed how influence operates in the digital public sphere. As users increasingly rely on platform-specific news feeds and partisan outlets, concerns have grown that selective exposure may limit citizens’ ability to engage with diverse viewpoints and resist misinformation. This study conceptualizes diverse media use as a key dimension of digital media exposure that shapes how individuals encounter information across contrasting communicative environments. Drawing on a national online survey of South Korean adults (N = 1,000), this study differentiates media platform diversity and media partisan diversity and examines how each is associated with political knowledge and conspiracy beliefs about the #MeToo movement. The analyses reveal a dual pattern. High levels of platform-diverse news use, while seemingly satisfying users’ information needs across different platforms, were unrelated to political knowledge yet positively associated with belief in #MeToo conspiracies, suggesting that cross-platform repetition may amplify misinformation rather than broaden understanding. These findings indicate that users exposed to news across multiple platforms may develop a perceived sense of being well informed, even in the absence of substantive knowledge gains. In contrast, higher levels of partisan diversity in digital media use were positively related to political knowledge and negatively associated with conspiracy beliefs, pointing to the potential of ideologically diverse exposure to support more balanced information processing. Overall, the study extends ongoing discussions of media diversity by demonstrating that greater exposure across platforms does not necessarily correspond to more informed or reflective beliefs. By highlighting how different forms of diversity shape belief formation, the study offers new insights into the subtle, system-level mechanisms through which digital information environments exert persuasive influence.