Realistically, the car will do fine in Colorado. With my 08 Impreza every day in Denver, I operate with roughly 145 hp due to elevation which is more than adequate for dd, even at 10-11,000 ft (loaded up with roof basket) I only operate with roughly 115-120 hp which is plenty fine. It is no rocket by any means but never complain.
I understand the Impreza and XV have lower hp to start with but compare the XV CVT with the Outback 2.5i CVT. The XV weight is roughly 3150 lbs with 148 hp while the Outback 2.5i is roughly 3450 lbs with 170 hp. This yields 21.3 vs 20.3 lb/hp respectively. Also consider the Outback has more cargo capacity. Now there are plenty of Outback 2.5i in Denver and commuting in the mountains. The 3.6R or turbo are much more effective at altitude but not a necessity.
Sure the XV can use more power and a diesel option would be welcome but understand the XV is NOT a performance car. Don't blow this out of proportion.