That's not exactly what McLuhan meant by that statement. "The medium is the message" refers more to how the medium itself influences the way a message is perceived by an audience. It is not an assessment of the creative process itself. It's not as though I disagree entirely with what you're saying though. There are certainly ways in which the medium is highly influential over the process of creating something. But it's a mixed bag, and technical skill is not something to be celebrated in all cases. A technically accurate painting is oftentimes quite dull and uninspired. One could argue that creativity isn't just the interaction of skill and mind, but rather the ability to think beyond the medium, to embrace accidents, imperfections, and impulsive decisions.