Is the author seriously telling us he went in there with no plan and on top of that sent most of his men to die for nothing….
This reflects poorly not only on the MC, but also Maou, who is a reincarnation of a warlord who is supposed to be knowledgeable about this stuff.
Losing is fine, even getting outmatched is fine, but just having the character uncharacteristically job is poor. (Though admittedly writing a good losing battle for your MC is not easy)
If you know you’re numerically disadvantaged, you don’t march in without caution everywhere with all your troops, if anything you would try to guerrilla your way against the enemy.