Nitrox is oversold but on a different premise: that divers get less fatigued diving on Nitrox. I've read this multiple times on Scubaboard and heard again on a boat recently.
I'm fulling willing to admit it could just be a placebo effect however, I usually do feel less physically drained after doing multiple dives on Nitrox then I do on air. I don't dive it for that reason, I dive it for NDL gains and purely for NDL gains, that just happens to be a perceived side effect.