Gerrymandering is not about creating hyper-majorities. That would be counterproductive - votes above 50% are wasted. It is about maximizing number of likely seats. Also the country has sorted itself geographically (e.g. cities vs. rural) along ideological lines, so non-gerrymandered districts might as much if not more one-sided.

[1] http://www.washingtonpost.com/blogs/wonkblog/wp/2013/02/17/r... [2] http://www.newrepublic.com/article/114989/government-shutdow...

[Edit] Hyper-majority may be a result, but not on the side controlling redistricting: the opposite side may be gerrymandered into few concentrated districts.