She does a little more than just whack the ball hard. She has very deep, fast, accurate shots and one of the better serves. That's enough to beat just about anyone ranked outside the top 10 without much of a sweat if everything's working.
And please note that depth and accuracy won Chris Evert 18 GS singles titles. Power, with depth and accuracy, won Monica Seles nine GS singles titles. Neither of those players liked coming to net. Neither was the best server of their day. Neither was a great
volleyer, though both were adequate if forced to come to net.
Sharapova needs a better head for controlling the point, and keeping opponents from expliting her relative lack of footspeed. And like most very tall players, if you get her running from side to side, it's tougher for her to reverse direction than shorter players.
But saying all she does is whack the ball betrays a certain ignorance,or lackof observation. The best example of a player who ALL they did was hit the ball hard is Jennifer Capriati. She did NOT take risks. She just got back every ball, and made sure she whacked the hell out of it. And won three slams that way.
Sharapova is certainly one of the four best players in the world right now, and the reigning US Open champion. That implies that her deficiencies, whatever they may be, are not that easily exploited.