As I said, no system is perfect, and no system tells the whole story. Your eyes tend to be a better test. My opinion though is that in the end, passer rating tends to match up most of the time to my eyes. In my head right now, without looking up the numbers, I'd say there are around 16 quarterbacks playing better. Tannehill is 18th in passer rating. It matches up. But then again, Cam Newton is one of those 16, and he's 26th in passer rating (mainly because his completion percentage is awful) right now. So, it definitely doesn't tell the whole story. It's just a tool.