Do prunes in our hands and feet not an example of osmosis?
The pruning of our hands when they are in water is an evolutionary trait that helps to increase our grip in when conditions.
The pruning of skin on the hands and feet only happens there, and is an evolutionary trait that increases the surface area of your skin and helps your hands and feet to grip wet surfaces more easily. It has nothing to do with osmosis, or else every surface of your skin would do that when in contact with water.
I think the dead layer of skin that makes up the outer layer of our skin help to prevent passage of water (not sure mechanism, but probably has to do with keratin protein).