No, the layers are where the actual work goes. Think of it like s stack of paper. Each piece of paper is a layer.
Now Screen is a blending mode. You can change each individual layers blending mode to screen or any other style. Think of the same stack of paper. Now remove one sheet but replace it with a piece of tracing paper. Still the same stack and amount of pieces of paper (layers) but one sheet, the tracing paper (Screen) would look different and any art on it would look different.
Hope that helps.