Christian Gartmann, from the High Engadine flying club, said the pilot was free to choose his own route according to the weather, wind, air traffic and other factors.
Box canyon?
That must have been well above 10,000 density altitude.
With that load your climb performance is a couple hundred feet a minute....if that.
The slightest downdraft will put you in the rocks.
Reminded me of this accident:
https://youtu.be/LzDSq6m2zV4