But again. let's look to Occam's Razor or, if you prefer, the Swiss cheese model. What scenario needs fewest number of slices of Swiss cheese to line up for the outcome we have seen? We know the plane wasn't flying on autopilot, we know that there was moderate freezing forecasted in clouds between 5000 and 10000 feet, we know he was climbing to 10000 when the incident started. Icing was therefore likely to have been present.
We know nothing of what/who was flying at the time of departure. We don't know that the aircraft even entered cloud to gather ice. Wandering heading could be the pilot using heading mode to avoid small buildups, the fluctuations in speed and rate of climb could be mechanical turbulence outside cloud and the changes in ground speed can be attributed to wind changes aloft as the aircraft climbed, which would also cause turbulence at the shear layers. We just don't know. The lack of radio calls more suggests everything was normal until it was not, then they either could not or were too busy to make one. I know that ice does not suddenly turn an aircraft into a brick, I have hundreds of hours in icing, some severe events. At all times I had time to talk to center and exit the conditions.
At the same time, I wouldn't blame a pilot who became incapacitated due to an unknown medical condition as being guilty of pilot error because, after all, none of us know when our time has come. It's not a crime to become involuntarily incapacitated, it's not as if the pilot said "yes please, I want a massive stroke / heart attack right now...." If it happens, it happens - why do you believe we mustn't consider such issues as most likely but rather want to suggest BRS malfunction or some other mechanical reason for the accident?
Pilot incapacitation has more far reaching implications than just simple pilot error. The whole AvMed premise of restricting medicals is based on the rates of accidents attributed to incapacitation, so the higher the rate, the more justification to place more restrictions and tests on pilots, which don't make flying any safer as we all know underlying conditions that tend to kill you stone dead are very hard to detect, even heart attacks occur over time. A stroke is almost impossible to predict and could be the result of you sitting watching TV too long the night before in an awkward position. And personally I don't 'want' to find an answer, I want to know the answer, no matter what it is. Whatever the truth is here will add to the learning files for all who come after, so squeezing the accident into one cause that is what everyone wants to hear is not going to help stopping it again.