That depends on your definition of miserable. If it's, "they're not obedient, they won't listen" then yeah, you might be right. But I happen to think, depending on ages here, those can be desirable qualities and are a natural state of childhood in the absence of fear/corporal punishment.
If we adjust our expectations, one more consistent with reality and not culture, children behaving like children is OK. We have to remember they're independent beings, just as we are, whose needs and preferences have equality; and not inferiority just because they're children.
Maybe you can elaborate on how exactly the results were miserable? And let's also not mix and match here, did they truly parent consistent with the ideas in the video? Or did they just not spank, but also didn't give a shit about or pay attention to their kids? There's a big difference.