"Had the army not been well led, the losses would have been even heavier (as they were for all the others) and we would not have won."

Without commenting on the veracity or otherwise of this strange remark, I'd just point out the illogicality of it. The easiest way would be to turn it on its head, thus: "Even though the army was very badly led, our enemies' armies were even worse led, leading to heavier losses for them than for us." Just saying.