Best single model
Simple two-model fusion
Weighted fusion
Three-model fusionOnly when complementarity justifies the added model.
Class-specific weightingOnly after simpler weighting demonstrates repeatable value.
Meaningful reproducible gain?
NO
Stop and keep the simpler system.
YES
Consider OOF learned stacking or gating.
Advanced learned fusionOOF stacking or learned gating only when complementarity and simple-fusion gain justify it.