If Plan 17 for the French during World War I was basically as simple as " Whatever the circumstances, it is the Commander in Chief's intention to advance with all forces united to the attack of the German armies," how bad were plans 1-16?
Here is a previous answer by u/vontysk that talks about previous plans.
More can always be said, of course, but the change in plans reflected changes in strategic, intelligence and diplomatic developments (for instance the formalization of the Franco-Russian alliance or the acquisition of German battle plans). In other words, it wasn't that the plans were bad; they were just bad after things changed in Europe