Every surface is unique. Sometimes a dusting of new snow over smooth ice is even more slippery than just the ice, and a few hours later it is much different. The only way to judge a given surface is to test it by walking on it or driving very slowly and testing your brakes.
Snow at least give the tires something to "grab" on to.
A sheet of straight ice is basically as slippery as… Ice. Regular tires on black ice have close to zero grip. Like if the road is cambered, you just slide into the gutter. A layer of snow at least gives you "some" grip. You still need to be super careful of course.
In general, tires perform much better in snow compared to ice coverage surfaces.
If you have the right tread, it can grab snow easier than just bare ice. If you had nail studded tires those would grab ice.
Snow. Driving on fresh snow isn't too bad. It's the day after when the snow has been flattened and then freezing makes for the dangerous roads.
snow over ice