How perfect is Voynichese?

[oshfdk]

And now we ask ourselves the question - why should the Voynichese be a clear cipher? 

Because normally in a project of this size if one finds any problems there is plenty of time to sort them out. For example, one possible explanation of the missing q in the first 1.5 pages of the manuscript could be that some problem (ambiguity or just inconvenience) was identified and fixed by adding a new character.

And, conversely, I find it less likely that a 240+ pages long manuscript was (seemingly) completed while using a badly designed system.

Why do we believe that the author was so brilliant and talented that he created a great undecipherable method unknown to science?

It's not necessarily about being brilliant, but the author most likely had some out of the box thinking. Look at the images. There are plants, nymphs, star charts, animals and strange diagrams, hundreds of images. Some of them contain seemingly known symbols, many of them appear to refer to some known scenes or existing medieval stock images, but in a heavily reworked way. With the exception of the Zodiac, not one of the images was certainly and positively identified, and even for the Zodiac, we don't really know what the charts mean, but each of the images appear to mean something. The author of the manuscript managed to fill the whole book with images that elude simple identification. Whether they are just decoys is not important here, but the author certainly had some imagination.