That's the issue with many of the lens review sites, they manually focus lenses to test their best acuity, but do not test the autofocus very well.
Third party lens manufacturers have a really difficult situation with autofocus systems. Fore example, the lens must identify itself to the camera as a particular canon lens, but canon does not make anything close to this.
Each Canon camera recognizes the lens attached from the lens code, and may make adjustments based on that information. This can cause nasty things to happen. I think Zeiss has the right idea to stay away from reverse engineering autofocus.