  We re-examine attempts to study the many-body localization transition using
measures that are physically natural on the ergodic/quantum chaotic regime of
the phase diagram. Using simple scaling arguments and an analysis of various
models for which rigorous results are available, we find that these measures
can be particularly adversely affected by the strong finite-size effects
observed in nearly all numerical studies of many-body localization. This
severely impacts their utility in probing the transition and the localized
phase. In light of this analysis, we argue that a recent study [\v{S}untajs et
al., arXiv:1905.06345] of the behavior of the Thouless energy and level
repulsion in disordered spin chains likely reaches misleading conclusions, in
particular as to the absence of MBL as a true phase of matter.
