I was thinking that James' flatness in Budokan is really just a result of his lost power, rather than lost range.
If you listen to the older recordings from the Images tour, James would sometimes enter some notes slightly flat, and then he'd just power through them and it'd still sound pretty good. Or James would sing all over the place, sometimes wildly imprecise, but his power would allow him to jump around until he got to places where he could really belt.
James doesn't really have that capability anymore. Most of the time he can still hit all the notes he used to hit, but he doesn't have the same power to push those flat notes he's always hit over the hump, nor does he have the same ability to hurdle around notes via improvisation. So wherever James lands, that's where he stays. This leads to some pretty awkward moments like the chorus of "Blind Faith" on CiM where James is completely flat. Yeah, James '92 might have landed flat on that note too, but he'd also have turned it into an (almost) atonal screech before he was through with it.
James has never been the most consistent singer, but until the vocal accident, his vocals were so powerful that he could work around all that. Now his voice is actually much more precise and controlled than it used to be, but he just doesn't have the power to make up for those occasional tendencies to sing flat.