Im not sure why you would say that.
Its mostly about 35F at night at upper elevations around 11500 in July-Aug, but it will get down to 25 F occassionally.
Guitar lake is notoriously cold due to katabatic wind. Frigid air from Mt. Whitney at 14500 flows downhill .
Not uncommon to be in mid 20s on Mt. Whitney in the morning, all summer long.
So yes, UL down garments are the perfect hiking accessory. Not for hiking, but to have with you for when stopped. Mornings warm up quickly, and you only have a couple at really high elevation. Days are 14 hrs long, so the best thing to do is sleep in until sun is up around 7 am. No need for early morning cold starts.