Return allows Doryuuzu to hit Rotom-W, Randorosu, Gliscor, and Birijion, all of whom don't take much from Rock Slide or X-Scissor.
Really, the only reason why you would run X-Scissor would be to hit Celebi and Shaymin, and even then both take a lot of damage from Return (a +2 LO Jolly Return...