Problem is they're working backwards. They know Zipfs law is a thing so they know their gibberish producing technique should follow it.

They're going to need to be able to produce known hoaxes from the time period of the Voynich manuscript that have gibberish following Zipfs law when it was unknown for their claim to have any shred of legitimacy.

Yes, some papers elaborate on this, but the most recent studies on this (like the ones presented in November on the International Voynich conference) make clear that it is not some man-made gibberish.

It also makes absolutely no sense to spend such amount of time (and parchment) for such a hoax in the early 15th century. Who would be the audience? An early modern hoax made by alchemists to swindle Rudolph? This sounds imaginable, but not for the Voynich Manuscript which is without doubt a product of the early 15th century.