I think they were pertaining to how they had more brain and power because they lost the war
It's literally 1950, every country thought like that
not everything a character says is a reflection of the author
I know this comment is old but when he said
"They were more advanced in terms of brains and power", he meant military power (sheer numbers) and by "brains" he was referring to technological advancement (military equipment, resources, raw materials like steel). He was not saying this on an individual basis, he was reflecting on the state of the 2 countries during WWII.
This is an objectively correct statement. Imperial Japan was aware that they could not endure a long war against the US due to thinning resources.
The story seems like it'll be super interesting but first off, dear author, do you suffer from racial inferiority complex? What do you mean by more advanced in brains and power?