All-solid-state lithium batteries have the potential to provide increased energy and power density compared to conventional lithium-ion batteries with a liquid electrolyte. The charge transport within solid electrolyte-based composite cathodes determines the C-rate capability and ultimately the overall performance of a solid-state cell, making it one of the key remaining challenges. In this study, the charge transport in composite cathodes composed of Li6PS5Cl and NCM-622 is analyzed and characterized in terms of the effective ionic and electronic partial conductivities. The correlations between these effective conductivities, the microstructure of the composite cathodes, and the all-solid-state cell performance are revealed. By quantifying these correlations, bottlenecks for charge transport in composite cathodes are identified and strategies to optimize the cell performance are developed. The optimization potential of these strategies is demonstrated exemplarily by tuning electronic and ionic charge transport pathways using high active material loadings and an adjusted solid electrolyte particle size, respectively. The results will help to further increase energy and power density of all-solid-state batteries.