I haven't read the NTSB report, and only skimmed over recent posts to see if I was taking this out of context, but...
400 ft per minute downdraft would not make the aircraft uncontrollable. Turbulence might. But all he had to do to avoid a crash was turn away.
...with any mountain experience at all (and the gentle rolling hills of Scotland don't count
) you would realise you've just described the typical day out which ends with bits of brain splattered all over the granite. To wit:
400 ft per minute downdraft would not make the aircraft uncontrollable
-400fpm (approx. -2m/s) is very bad news at high density altitudes, such as your typical summer mountain environment.
Strong winds + mountains = rotors. Plenty of ways those can kill you, incl. losing consciousness following a sudden meeting of cockpit and skull.
But all he had to do to avoid a crash was turn away
One needs to appreciate that at high density altitude if you're lucky you've got 50% as much engine as at sea level, while at the same time you require a bigger turn radius. If you happen to be on a downdraft your available turning space will be reduced both horizontally and vertically, more so the longer you stay in the downdraft. Pulling a successful turn in the mountains requires experience, but that same experience will usually stop you from getting into a situation where you need to contemplate that sort of thing. I can remember two recent accidents (within the last 18 months) where non-mountain pilots and their passengers got killed just that way.
So yes, the conditions you describe can easily kill any pilot regardless of experience and no, you can't "just" turn away, because it doesn't work like that.