No, the argument being presented is that the humans of the 40k fictional universe, by virtue of possessing any form of active psionic ability (or latent for that matter) are not really anything like the humans of reality
I am not going to argue that everyone posses inactive psychic ability, and active one much less so, but in the context we are discussing here, which is Warhammer 40k universe, humans possess innate inactive psychic ability, as do nearly all living things, with some of them possesing active psychic abilities, which means that if, theoretically, Warhammer 40k were to be actually real, you wouldn't really differ from the regular people, which is contrary to this assumption:
You... what? Real, modern-day humans aren't psychic. If you existed in WHAOK-verse, the imperials would hate you for being a blank, because you have meat brains rather than soul. So yes, WHAOK humans are very different from real humans.
Unless you were actually a blank, but in that case it'd probably be evident by now because you'd have to have no friends, your family would hate you and it was horrible in general, although you could just be an asshole and achieve the same effect.
(and I'd argue very heavily that their culture and behavioral norms are utterly divorced from any form of reality as well, but that isn't really a discussion suited to this thread).
I'm wondering whose cultural and behavioral norms do you consider divorced from reality. I mean, apart from the whole Warp magic stuff, which cannot really be compared to reality and which is pretty well anchored in the Warhammer 40k universe reality, I don't think there is anything you could point to as being unrealistic. Racism, warrior culture, religious fanaticism and militancy, corruption, wastefulness, etc. is what humans did through the entire history, and I'd say that our actual history is pretty grounded in reality, as it literally fucking happened.
Of course, you might feel like that they are insane and unhinged, but that is only you live in modern times where survival, at least in western, developed countries, doesn't require the same drastic measures as survival in the Grim Darkness of the Far Future.