In golf a teaching maxim is "feel is not real." I think that may apply here as well.
No doubt Johnny Mac feels a wrist flick, but we know from highspeed video that what John Yandel says is true. But John only took us up to impact. If you follow a top (male) pro's swing, you will see that wrist flexion occurs pretty soon past impact. In fact, wrist extension at impact is somewhat less than at the start of the forward swing. So the wrist is slowly flexing during the contact interval and that flexion increases dramatically after contact. Now of course, I am not saying that wrist flex is used to generate power. I think John is correct that it provides directional control predominantly, but I think trying to maintain a fully laid back or extended wrist is also wrong.