It doesn't necassrily have to be a big part of the game. While variable winds are always a problem, there are steps to lower the risks with variable winds.
This advice may only to apply to my area of Michigan, where we don't have true big "bottoms" carved out by major river floods like much of the Midwest, as much as we have "bowls" or deep depressions in the landscape.
A key is, stay out of "bowls" and "bottoms" when variable winds are an issue. Simply don't hunt them on such days.
This is counter-intuitive for many guys, because many hunters often make the mistake of thinking a bowl/bottom will offer some shelter from variable winds. Often, with swirling winds, it's the last place one should decide to hunt. It's just the opposite.
While bottoms have a great lure for hunting, because that's where the deer often are, they can lead to endless problems on days with such winds.
You're better off to set up accordingly on the ridge tops on such days. If you're anywhere below the lip of "the bowl" on variable wind days, your scent will swirl and fill the entire bowl, or bottom, especially with evening thermals added to variable winds.
Granted, being on the top has it's problems with evening thermals, but if set up a ways from the lip of the bowl, and more on the center of a larger ridge top, you can mitigate the entire bowl/bottom from being loaded with your scent.
Basically, it reduces your overall "scent footprint".
I don't know if you can visualize what I'm saying, but I've found this approach to be much better on variable wind days.
Also, with thermals, there are some bowl/bottom/ridgeline area's that are virtually unhuntable because all you'll end up doing is spooking deer. With some bowl/bottoms, they're so conducive to swirling, you're better to completely stay out of them and make your "ambush plan" based on when the deer come out of that bowl/bottom.
Hope this makes sense.