The main point they author is making is:

"the prevalence of a single, monocultural aesthetic that seemingly almost every startup and tech company and would-be industry disruptor out there has adopted, it’s worth wondering if there’s some other voice—or even a different modulation of this same voice—that could be appropriate."

This, of course, extends far beyond illustration (the topic of the article - the examples provided are striking). I would love to see more variety - especially for styling UI components because I think we can do so much better than Material Design/Metro or Bootstrap.