You have to be careful with this. See Free Kriegsspiel is a wargame, developed by the General Staff of the Prussian Army. It is called 'Free' because the earlier Kriegsspiel (trans 'Wargame') was a fully closed rule-based TT game where the referee basically just adjudicated 'fog of war' (who can see who). This proved largely useless as an actual training device. So the Prussians gave the referee more power, hence the adjective 'Free', and this would also in principle allow the opponents to try open-ended stuff. There is still a very large and thorough rule book, but the referee was allowed to 'adjust' the rules in order to take account of situations that were not adequately covered by the written rules, to judge hard to quantify valuations like the effects of morale, etc. Note that these referees were HIGHLY trained Staff Officers of a working army, and the subject matter of the game was ONLY military operations. Thus the referee is the equivalent of a PhD level expert on the whole subject matter of FK!
There is certainly a line that can be traced from FK referee to D&D referee/GM, but there are huge differences, which apply to any TTRPG. The biggest one is that the referee cannot possibly be a complete subject matter expert, especially on the subject of an imaginary magical world! The subject matter of RPGs is simply too vast for that.