Quote Originally Posted by Uchiha Barles
The amount of chakra that can be outputted by a ninja is determined by whatever biological system that transfers chakra out of the body. To illustrate what I mean, take an electrical signal generated by a neuron. The signal is propagated by a change in the concentration of ions along the neuron (very simplistically speaking). Once a signal has been passed, another one cannot pass until until the ion concentrations return to their "pre-signal" concentrations. The speed at which this happens depends on the person (again, simplistically speaking). A similar thing could explain why one person is able to output more chakra than another. Maybe the number of outlets from which chakra can leak differs by ninja. Maybe there's strain associated with leaking out chakra, and the amount of strain that the chakra vessels can take also varies per person. A combination of these two would explain why training on the rasengan made Naruto's hand numb and blistered and what not.

So basically, this takes the X variable you mentioned and makes it static over short periods of time, by making the Y function determine that chakra replenishes at a much slower rate. The Z function would be a determined by the specifics I speculated on in the previous paragraph.
I agree with this since most of what you say is actually supported in one way or another by facts from the show. So Yuki's formula and your theory could technically explain everything but it really doesn't mean much if Kishi doesn't explain it himself. Besides like Archangel said there is also the BS factor to consider.