Demand forecasting in competitive and uncertain business environments requires models that integrate multiple evaluation perspectives, not just hyperparameter optimization using a single metric. This paper proposes the Hierarchical Evaluation Function (HEF), a multi-metric framework for hyperparameter optimization that integrates explainability (R2), root mean square error (RMSE), and mean accuracy (MAE). Using the Walmart, M3, M4, and M5 datasets, we optimize the model using Grid Search, PSO, and Optuna, and demonstrate that HEF outperforms single-metric reference functions. In particular, HEF excels in heterogeneous monthly time series (M3) and granular daily demand scenarios (M5). HEF improves stability, generalization, and robustness at low computational cost, contributing to improved model selection, supporting accurate demand forecasting, and supporting decision-making in dynamic and competitive business environments.