This is a similar situation to what pertained with the diesel hydraulic (Voith) DMU transmission in TS20xx, Class 158's etc. Each notch other than full power simply acted as a speed cap, therefore little more than glorified model railway DCC style (aka arcade) implementation. I haven't tested for this effect in TSW yet, but it is done so badly in TS2017 in that if you're running downhill but open the throttle to Notch 3 or Notch 4, the speed will actually *reduce* to the cap set for that notch, instead of adding to the momentum slightly.
If this is the core element of Simugrapgh, we're doomed! (Or saving the pennies to buy Run 8 V2).