Absolutely 100% disagree about the 'legitimacy' of Rice's mark. You might argue that his shooting might drop slightly on the new role, just like you might argue that Johnson's shooting would suffer because he doesn't have a comparable playmaker giving him looks.
And there are times when the differences between eras should be examined and taken into account, but usually I think those are most pertinent when addressing quality of competition. But, in this case, a mere what, 5 years apart, you can hardly dismiss Rice's mark as illegitimate. That is, unless you can somehow prove through shot location and other factors that Rice at that age, at that mark, wouldve been less effective.