Conventional graphitic carbon nitride (g-CN)/graphene supercapacitor hybrids are fundamentally limited by aggregation-driven loss of interfacial coupling and poor processability at meaningful solids concentrations. As a result, scalable fabrication of electronically integrated g-CN/graphene architectures remains elusive. Here, we demonstrate that highly concentrated (100 g L−1), solution-processable g-CN nanosheets (Sol-GCN) enable intimate and stable coupling with exfoliated reduced graphene oxide (rGO) via a rapid liquid-phase, acid-assisted co-dispersion/precipitation route. The optimized 1:5 Sol-GCN/rGO hybrid reduces charge-transfer resistance to 0.62 Ω and yields a specific capacitance of 620 F g−1 in a symmetric aqueous device. The electrode achieves an active material-based energy density of 21.5 Wh kg−1 while maintaining >99% coulombic efficiency over 16,000 cycles. Electrochemical and post-cycling structural analyses reveal that the enhanced performance stems from an increased electrochemically accessible surface area, strong interfacial coupling, and preserved structural integrity during prolonged cycling. Notably, the performance enhancement occurs despite a lower BET surface area than pristine rGO, demonstrating that electrochemically accessible mesopore transport pathways and interfacially coupled redox-active nitrogen sites, rather than total surface area, govern charge storage. This work establishes a scalable, metal-free, high-solid liquid-phase strategy for strongly coupled g-CN/carbon nanomaterial hybrids and challenges the conventional surface-area-dominated paradigm in carbon supercapacitor design.