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This study aims to construct a fully data-driven and reproducible Southeast Asia Influence Index (SAII v3) to overcome biases from expert scoring and subjective weighting, while mapping the hierarchical power structure across the eleven ASEAN nations. Methodologically, we aggregate authoritative open-source indicators across four dimensions—economic, military, diplomatic, and socio-technological—applying a three-tiered standardization chain (“quantile–Box–Cox–min–max”) to reduce outliers and skewness. Weights are obtained through an equal-weight integration of three methods: Entropy Weighting Method (EWM), CRITIC, and PCA. Robustness testing is conducted using Kendall’s Tau, ±20% weight perturbation and 10,000 bootstrap iterations to ensure robustness. Additionally, ±10% dimensional sensitivity analysis and V2–V3 bump chart comparisons were conducted. Results indicate the integrated weights are approximately: Economy 35%–40%, Military 20%–25%, Diplomacy ≈20%, Socio-Technology ≈15%. The overall landscape presents a “one strong, two medium, three stable, and multiple weak” pattern, with Indonesia, Singapore, and Malaysia leading, while Thailand, the Philippines, and Vietnam form a mid-tier competitive band. V2 and V3 rankings showed high consistency (Kendall’s Tau=0.818), though minor mid-tier reordering occurred (Thailand and Philippines rose, Vietnam fell), indicating V3’s greater sensitivity to structural equilibrium. ASEAN-11 average sensitivity further highlighted military and socio-technological dimensions as having the greatest marginal effects (±0.002). In conclusion, SAII v3 achieves algorithmic weighting and auditable reproducibility methodologically, empirically reveals multidimensional drivers of influence in Southeast Asia, and provides actionable quantitative evidence for resource allocation and policy prioritization by regional nations and external partners.