Let's remember that gerrymandering can work both directions. It's done as often to confine the opposition to one area and thus only one win (allowing your more spread-out voters to have a greater impact) as it's done to give anybody a safe seat.
Note: the above is not stated as a rebuttal to anybody's particular point...just thrown into the discussion for consideration. The fact that a district is heavily gerrymandered does not mean that the party that won it is the "guilty" party.