When I tried to make toon shading, with diffuse bsdf, shader to RGB, color ramp, and material outputs nodes, it appears to be fine if there is no object covering it with shadow(with only light emit and create the shadow)
but when there is something blocking the object and create a shadow depend on where the light, it will appear with some gradient
(the light is behind something, causing the floor to have gradient)
all object have the same nodes, only diffuse, shader, color ramp, and material output.