I'm experiencing this issue as well. I've spent a couple of weeks scouring the internet and asking questions in various places, and it's as though nobody's noticed this or thinks it's a big deal. I guess 99% of people don't use their eyebrows for emoting? All I can assume is that the hype around the ARKit face tracking was coming from hobbyists who played with it like a toy, and that it actually has no real usefulness as an actual indie-professional solution. Happy to be proven wrong, but I'm already in the process of setting up a production pipeline using Faceware instead.