For drought tolerance, is water use efficiency (WUE) no longer a recommended selection criteria for energy crops?

Podlaski et al. conducted experiments with energy crops like miscanthus, prairie cordgrass, willow, etc, and report that  water use efficiency (WUE) is no longer a valid trait for selecting energy crops for drought tolerance. They could not find any significant relationship  between  WUE  and  biomass  yield. However, they found a positive correlation between  soil water storage and the biomass  yield, and the response was highly differentiated among the crops under various vegetation seasons. (Summary by Sridhar Gutam)  Photosynthetica 10.1007/s11099-017-0697-0