Benchmarking subset 1 consists of all the reactions with σ below 3.5 kcal/mol; subset 2 consists of all reactions with a higher σ. Comparing the performance of the different functionals, with respect to the DLPNO-CCSD(T) computed reference, between the two subsets, we observe remarkable differences, both in qualitative and quantitative terms (Fig. ). While the 3 best-performing functionals, ωB2-PLYP, ωB97M-V, and M06-2X are only negligibly affected by evaluating a different subset, the ordering of the remaining functionals changes profoundly. For example, the functional ranking in fourth place in terms of performance for benchmarking subset 1, ωB97X-V, drops 3 places when evaluated on subset 2. Remarkably, while BLYP and B3LYP are seemingly quite robust when evaluated on subset 1, appearing halfway in the functional ranking and resulting in an acceptable MAE of 2-3 kcal/mol, for subset 2, their mean errors almost triple (to 8-9 kcal/mol), rendering these functionals the second and fourth least reliable functionals of all the ones tested, respectively. Adding empirical dispersion corrections partially remedies the remarkable failure of these functionals, but even then, significant performance losses are still observed (cf. Section S3 in the ESI).