Surely the "moot point" thingie goes way back to the original meaning of a question that had remained unresolved by a particular "moot" or meeting, e.g. in the moot-hall or moot-house, or on moot-hill (not boot-hill, or at least, not usually) or whatever.

So don't worry about Garner and his "ambiguity", not to mention the lawyers. Forget "no practical significance" or such. Be not ashamed to use the expression properly. Long live vitality! (To coin a phrase).

Rgds, lusy