I was about to say what you said. Also you have to be close to grab and risk a lot more than shooting with the Schleuder. I think it's a bit too powerful to. Herec, Shae and Doldren also have stipulations on their weapons that prevent them from spamming (well the high damage ones, anyways), like one shot per reload with Harec, slow "reload" letting the pressure out with Shae which she can't do ANYTHING but walk while she does this, and it lasts a bit of time, and finally Doldren has to wait a moment for his gun to fire max damage and then only the first shot keeps his stress down.
I don't think one shots are the problem Draco, I think it's how EASY they may or may not be, the sacrifice a character has to make to do them and the relative weakness of that hero to justify the one shot. Ginebra, has no weaknesses with the Schleuder. At 100 health, resistant to gunfire damage, and the ability to go 0 to 60 in a split second, she is one of the best, if not THE best, character in the game.
EDIT: Also consider her other two weapons which ar balanced relative to her Health, resistance and mobility well. Default does crab damage but has push and does additional damage if they colide with other stuff. And Javalin does HORRIBLE damage up close and only "decent" damage afar, but only at max tension. With Shleuder you just have to shoot the ground in front of your target.