The crew are always responsible for terrain clearance, not ATC and had they been more situationaly aware of the surrounding terrain the crew would never have allowed that descending left turn while within the valley and below the level of the surrounding peaks.
Of course the crew is responsible, as it should be.
Approach briefing (or lack thereof) my foot....the respective crew simply did not follow the mandated procedure...no more, nor less.
That the crew accepted a last minute change, is no excuse.