Win ratio on rumble might mean something as that is free for all, there's no teammates carrying you, or dragging you down whichever the case may be. But win ratio on team based modes can easily be padded by playing with a good team that can carry you, regardless of how bad you are. Someone with a 0.5 kd may only play with his friends and have a really high win percent because they carry him, but individually his stats aren't good