What they says is true, however.....
Yes the difference in discharge rates can be a problem especially when using two values to make another. For instance using a 5uF and a 15uF to make a 20uF value. This does cause a smearing effect.
And I can use my Clio measuring system to see the phase shift that occurs from the dissimilar values.
However, using a by-pass cap of a .1uF or smaller puts the phase shift at or above 20kHz. So hearing the phase shift is next to impossible.
And there are clear audible improvements that can be had from properly by-passing.