Distribution of decay slopes d for 85 GRBs, fitted with a three-component Gaussian mixture model (GMM). Three extreme cases (GRB 070306, GRB 140209A and GRB 161004B) with d > 7.8 were excluded to avoid skewing the high-d tail due to potential observational or physical anomalies, and their removal does not affect the main results. The best-fit components peak at d ≈ 2.04, d ≈ 3.56 and d ≈ 6.04 with relative weights of 0.50, 0.32 and 0.18, respectively. Most events fall in the range 2 < d < 4, suggesting hybrid central engines, differing from idealised BZ (d ≈ 1.67) or NDAF (d ≈ 3.7–7.8) predictions.