The original article's claims, and your counter-claims, need to be proven/disproven by a study of individuals practicing poly-phasic sleep for e.g. 10-20 years. Until then, we're basically in anecdote territory.
I think it's because this is something that is very hard to stick with. After the physical adjustment, one has to be willing to organize one's life in a way consistent with this, and that is tough when everybody uses this other mode of sleep.
