Ehhhh...
If an S-rank can annihilate your army, YOU DO NOT MOVE YOUR ARMY until you know where the S-ranks are, or have an S-rank of your own to counter them. This would be standard military doctrine in this world.
That general does not have the basic common sense required by the setting; him being in charge at all is a plothole that needs explaining and lampshading.
It annoys me when authors do not take their worldbuilding to its logical conclusion...