Artistic ability of the VMs illustrator

[Searcher]

Skill level depends partly on available resources.
For example, there are many artists who can render a good portrait from a photo, while only a small percentage can do it from life, and only a tiny percentage from memory.
I have seen artist Robert Bateman trying to sketch something he had previously painted with extreme accuracy. Without his reference materials, he struggled on a  'stick drawing level' to sketch a simple outline of the animal from memory.

You are absolutely correct. I want only to add that every artist has favourite objects for drawing in the sense - most simple, felicitous for him. Human body seems to be more difficult in depiction for everyone. Not the least thing is a size of the image, it is always difficult to draw little images and little details, especially with a pen and ink. 
On the whole, I have an impression that the author depicts most of pictures quite carelessly, some details are more important for him than the accuracy of proportions, painting etc. Some details look deliberate careless, as for me.