"A full, rich drawing style is a drawback"

In this quote, Bill Griffith is recommending that a full, rich drawing design can be a negative aspect. He is implying that an extra detailed, elaborate style of illustration can be more difficult to achieve and can take longer to finish. Additionally, he may be suggesting that a more comprehensive design of drawing can be harder to comprehend and also interpret. He might also be recommending that a much more detailed style of illustration can be harder to reproduce and can be more time consuming. Ultimately, he is recommending that a much more thorough design of illustration can be a drawback in certain circumstances.