Did I miss something? The title and article are mostly about JPEG XL. What's the "both" in this? JPEG XL is the newest and has poor support. AVIF is mentioned offhandedly in that article, but it's a little older and still doesn't have great support. WebP is even older and also has occasional issues.

The image formats past WebP offer very minor improvements but have big potentials for new zero-days. I don't think it's wrong to play it safe and/or just don't implement them.