For variable winds often you need to mix the two extremes. A sail that has enough fabric to catch the light wind, but strong enough spars to handle the gusts. The sail will stretch out faster than it normally would, and you may need to dart to the edges whenever there is a gust, but at least you'll be flying.
Another alternative if you're flying long enough is to have two kites set up, when winds start to shift land the one and launch the other. I've had plenty of times where I had both a standard and a full vent set up. As wind changes I land, stake one the set of lines, then pick up the other. As conditions change back, I land, swap the kites, then launch the other.