Those are the exact actions the device has. It takes those actions using a default ramp rate that gives a pleasing fade up/down when used with a lamp as intended. You can adjust that ramp rate if you dig into the zwave parameters and instructions. I’m not sure if “instant” is an option though.
You’re thinking of wall dimmers with separate on/off button and slide to control the dimlevel. Electronic dimmers used in home automation are not that style. In order to enable the fade effect they almost always work on/off in tandem with dimlevel using a configurable transition time or ramp rate.
If you’re using it with non-dimmable lights, then you should look for the appliance module which is on/off only.