In the rapidly evolving platform economy, the competition between platform-owned products and third-party offerings is intensifying. This study examines the entry and pricing strategies of dominant e-commerce platforms such as Amazon and JD Mall which sell both platform-owned and third-party products. We use a complete information game model to analyze the strategic interactions between these platforms and third-party sellers, focusing on cost discrepancies and limited entry capabilities, areas previously underexplored. Our key findings include the following: (1) Platforms with dominant power can restrict third-party product pricing. (2) Increased consumer influence by the platform can reduce competition between platform-owned and third-party products. (3) Platforms prioritize high-value-product markets when entry capabilities are limited. (4) Commission-based revenue models are generally more efficient than entry fees. (5) Regulatory bans on hybrid models do not necessarily enhance social welfare; differentiated taxation on various revenue sources may be more effective. This study contributes by developing a comprehensive game-theoretic model to simulate strategic interactions, analyze pricing competition and entry strategies under cost asymmetry and capacity constraints, and provide theoretical guidance for regulatory policies.