"Beastmen are roughly 10x as strong" oh dear your calculations are way off. If the lady knight is correct the "queen ostrich" is roughly 1000x stronger although perhaps you can tone that down a tad if their troops are super elites to like 800x. And the little ones even if they're only 1/2 her strength that's still like 400-500x and there are a LOT of them.
It is always so ridiculous when manga presents one guy they claim is some tactical genius, and then make them overthink and make assumptions about the main character for the sake of the plot. It makes them look more stupid.