For example, even the creator of SuperMemo seems a fairly average person and not the polymath/hyperpolyglot one might have expected him to be (or at least I could not find any indication of that).
Likewise, what has David Allen actually done beyond writing the same book half a dozen times?
As far as I can see this stuff mostly exists to fill a need for structure, but it does NOT make one exceptionally productive (also accounting for the time that needs to be invested in the tools and techniques themselves).