I agree we should be very careful to preserve readability, but I find that site a little ridiculous. It's arguing that we don't have to sacrifice aesthetics for readability... and it's ugly as sin. "High contrast" pairings like #cfba58 on black don't help their case.
Readability is not just about contrast. In that very site, they also make controversial choices like pure white text on a pure black background, which is not universally agreed to be easy on the eyes.[1][2] Part of the reason I understand that there's been a movement away from 'pure white on black' as a standard for text is that high levels of contrast can be hard on your eyes with extended reading... such as reading long Wikipedia articles.