I don't think it's as simple as making a touch sensitive surface map for buttons. Take this for exampe: in Xbox controller, you can have you thumb touching "a"

I don't think it's as simple as making a touch sensitive surface map for buttons. Take this for exampe: in Xbox controller, you can have you thumb touching "a" and "b" at the same time, while you can either click "a" or "b" while touching another. Try doing that on a steam controller.