If we are saying Middle Earth is low fantasy, I can get behind the argument that GH is too. But I really don't think many of us think it is, do we?
Aren't magic level and high vs. low fantasy two different different things? Is a big part of high fantasy it's epic nature with big stakes. High fantasy seems to often be high magic, but can't you have one without the other?
Edit: Cook's Garrett files seem high magic but the crime noire setting doesn't feel high fantasy at all. Lord of the Rings seems lower Magic, but much higher stakes.