Howard, there is no doubt that a machete can get better penetration than a khukuri because of the thinner blade. The problem however as you noted is the binding and the relative fragility on harder woods. They do however have their place, as do all blades.
As for poor khukuris, this weekend I saw one that could probably be outchopped by a 3" hatchet. It was from India and looked to be stamped out of 1/8" stock but there indendations and fold lines in the steel. No real grinds to speak of, the "edge" was about 2mm wide.
-Cliff