Guetlzi comparison is mostly against JPEGs you can find in the wild (ie. from a digital camera). In my experience, Guetzli is a lot slowly than mozjpeg, but to

Guetlzi comparison is mostly against JPEGs you can find in the wild (ie. from a digital camera). In my experience, Guetzli is a lot slowly than mozjpeg, but tops up at much higher space savings when the conditions are right.