If you ride flat-out you need a layered system. If you can moderate your riding to prevent overheating at times then some built-in insulation is more convenient. When you are diving in and out of warm buildings after riding you need to shed a lot of layers rapidly and I find an all-in one winter jacket easier to handle.
I have 2 winter "softshells", a thin one for Oct-April and a thicker one for Dec-Jan.
Im not sure what counts as a softshell but both of mine have an insulated fleecy layer and a windproof/water-resistant outer lshell ayer.