Rushing isn't over powered its fine just the way it is.

The problem is that there are not enough defensive options. Turrets are under powered as they have blind spots and relitivily low health. They become targets to the rusher and are instantly destroyed. This does give time for the defender to work on a counter. Although this almost never works as the units are destroyed as they come out of the base or (if in lock down), the rusher destroys the barracks/depot/air pad haulting their production.

There are other sutlties but you get the point.

Basicly if you want to win and advance your true skill level then you are forced into playing either a rush game or using rush tactics defensively. This gets boring fast if thats not your prefered way of play.