In favor of soft rubbers we can argue with the “control” or better said the forgiving effect at the moment of ball impact. Even if the stroke is executed properly, it can still be played safely over the net. Due to the deeper penetration of the ball when hitting it, you have a better feel at a moderate pace.
Another point is that it is much easier to generate spin with soft rubbers. The ball can be guided “longer”. Especially with slow movement strokes, a soft rubber has clear advantages over harder rubbers. The strong catapult effect provides sufficient speed without much effort. Another advantage, that should not be underestimated, is the lower weight compared to hard rubbers.