It presumes that Picaso, Bansky, and Monet can't paint like each other.
Probably not true if you actually have Picaso, Bansky and Monet.
In any case, style guides are for hacks, not artists.
This is the style Picasso was told to paint in when he was learning to paint:
http://mesosyn.com/pp-early.html
It was only after he had mastered this conventional style of painting that he went on to discover cubism.
"When Picasso purged color from his work, he did so to emphasize the formal autonomy of the picture plane and focus on problems of form." [1]
Styleguides don't hinder creativity. They help it shine. It simply a set of constraints that help guide you through the creative process. Same as convention-over-configuration. Yes, you are forced to put certain files in a certain folders, but that just saves you time, it does nothing to stop you from being creative.
[1]http://galleristny.com/2012/10/from-brush-and-palette-to-pri...
Here's a simple question: what spurred Picaso's decision to paint in Blue? Was it adherence to a protocol describing blue as the answer to his expressive woes, or was it his own internal experimentation with the color blue?
Did Picaso paint in blue because he felt like Blue, or because someone said "any work 'submitted' to this gallery must be blue"?