I think the reason the ATP style forehand is so rare is because the WTA style is so much easier when you're first starting. Of course, when you get better it's a much riskier shot with a less desirable outcome, but by that time most players are not going to change. The WTA style is just pushing through the ball while rotating at the elbow. It's very simple in concept, but very difficult to control because it takes perfect timing and positioning. The ATP style allows the forearm and shoulder to store elastic energy as it lags behind and then when the arm comes through it allows players to create massive amounts of racket head speed. It also allows players to simultaneously increase the amount of spin with pace, rather than trading one for the other. It's a much more forgiving stroke, gives way more control, and gives you way more options. It's just harder to learn, so not many people bother. And also, yes, Raonic's forehand mechanics are bad and basically WTA style. He can't get spin without trading a ton of pace, similar to roddick.