Do you actually have any real world flying experience yourself or are you just comparing to high alt bases in AH?
I can only speak from helicopter experience but I would rather attempt to land on a fence post in a confined area at sea level then a platform at 9,200 feet.
Operating at high altitude means you are in high density atmosphere e.g thin air. Which means less lift and require more power. Operating at high altitude doesn't leave much power to spare if any in some situations.
That slope on the runway isn't that big a deal, fact that it's at 6,000ft is something put it at 9,000ft and difficulty is magnified again.
...-Gixer