Indeed, it is stated in Saito 2003: 1 that the hypothesis that Japanese scrambling is uniform makes the task of explaining certain properties of the 'scrambling construction' "more challenging."

What is referred to by "Japanese scrambling" is what is called the OS type construction in Ueyama 1998, 2003, plus the DO IO construction, and they are often regarded as constituting a set of phenomena, so to speak. Given a set of phenomena that exhibit some similarities on the surface, we do not know, a priori, that they are manifestations of, or due to, a single operation/relation/etc. Regardless of whether one might argue that "Japanese scrambling" is indeed a uniform phenomenon, one would need to provide a substantial empirical and conceptual justification for one's conclusion. Which conclusion/hypothesis one might draw/pursue, therefore, shouold not make one's task more or less challenging than the other, as far as I can tell.