In this case, the bottleneck might be any sort of technical issue such as our classifier choice, regularizer choice, data scaling, etc.
in order to validate our conclusions, we repeated the same experiments with different classifier choices (SVM, logistic regression, bagging ensemble of decision trees and AdaBoost); different regressors (SVM, neural networks, ensemble of regression trees and gradient boosting); and data scalings (max/min scaling and component-wise centering plus normalizing by the standard deviation).