I've had good luck with face detection on both my XT1 and XT2. Admittedly, I rarely use it, and only for certain occasions where there's only 1 person as a subject and they must be facing the camera. I've even used it photographing kids, with good success. If the subject turns too much to the side and the camera can't detect a face it reverts back to single focus point anyway. What lenses are you using face detect with? I'm wondering if mine works pretty good because I'm only using prime lenses and the system has more available light to work with, or maybe that doesn't make a difference.
I've only used regular face detection, not eye detection. The XT2 seems better after the new firmware, but it worked good for me before the last firmware update anyway.