I would think the manufacturers tag of 'All weather capability' would be backed up by some such phrase as when operated from and to suitably equipped facilities iaw with ICAO/EASA legislation. The civilian operation of 'all weather' would be very different to military or SAR for example.
There's plenty of talk on here of zero/zero profiles/capabilities, pilot IR experience etc, all irrelevent at the time of the accident, as this was a VFR take-off in VMC, there may or may not have been an intention to transition to IFR in IMC at some point after the take-off at which point crew qualifications and capability could be a subject of valid opinion.
To explain further, I've done plenty of zero/zero departures into IMC from suitably equipped airfields and i've done thousands of VFR take-offs from unregulated unlit field sites, but never an IFR departure/take-off from a field site.....the take-off has always been VFR with a suitable planned transition to IFR in IMC (or VMC). I imagine that is the experience of most on here?
The point I'm trying to make here, is that this was a VFR departure, it had to be, so talk of the 139s complexity and pilot IF experience is not valid.