Maybe to acknowledge that "functional" is used with a different meaning, often, would be sensible rather than just pretending all one needs to do is re-define i

Maybe to acknowledge that "functional" is used with a different meaning, often, would be sensible rather than just pretending all one needs to do is re-define it from common usage and proceed. People are not compilers. If you want to redefine a word that is already in your readers' vocabulary with a meaning ascribed you've kind of got to talk about why you're doing that and why your redefinition is worthwhile and the alternative, generally accepted meaning needs to be jettisoned. Or you risk unintentional impersonation of a crank, which would be a shame if you're actually correct.