Whilst I appreciate that the ability to maintain a given heading/track fine tolerance is important in certain IMC departures, mainly runway, surely no-one here can actually think this is particularly relevant to this accident? If there was any pilot error from disorientation on climb out/transition it would have almost certainly come from the basics of not keeping wings level and pitch controlled appropriately, would it not, which should have been the main focus.
I am more interested in how this phase would have likely been carried out - was it hand flown or coupled autopilot upper modes? What is the 139 like to hand fly in pretty much zero zero conditions?