Value-Flow Symmetry and Sustainability in Digital Innovation Platform Ecosystems: A Heterogeneous-Actor Lotka–Volterra Analysis

Digital innovation platform ecosystems can scale rapidly without becoming durable because broad participation does not ensure sustained value circulation. Existing models homogenize complementors, obscuring horizontal coopetition among distinct groups and its interaction with vertical governance. We examine how vertical and horizontal relations shape value-flow architecture and sustainability. Drawing on ecological symbiosis theory, we distinguish a platform orchestrator, technology-extending complementors, and service-integrating complementors. We construct an extended three-actor Lotka–Volterra model and use the Global Value-Flow Symmetry (GV) index and the continuous directional indicator δc to assess symmetry and direction. Designed for theory building rather than empirical calibration or testing, the analysis uses no empirical data and compares 35 vertical–horizontal configurations through deterministic simulation and sensitivity analysis. Results show the following: (1) Greater symmetry is associated with higher aggregate maintained output, but vertical backflow direction shapes its distribution; GV must therefore be interpreted with δc. (2) Under complementor-favoring vertical parasitism, horizontal mutualism expands complementor output but intensifies negative vertical backflow, simultaneously increasing aggregate output and reducing platform equilibrium—a cooperation paradox. (3) The same horizontal mutualism yields three focal outcomes across the examined vertical structures: Negative complementor-to-platform effects produce the cooperation paradox, absent effects produce value decoupling, and mutually positive vertical exchange produces systemic resonance. Thus, horizontal cooperation does not necessarily enhance sustainability; its effect depends on whether complementor gains feed back to support platform capability. This study advances platform-ecosystem sustainability research and offers theoretical guidance for optimizing value backflow and cooperative governance.