Starchy tubers are only one of many possible choices for carbs at the Performance Level. You've also got fruit and vegetables. In our experience, we've found that through the process of eating and relying on a higher percentage of calories from protein and fat, your body adapts to utilizing them, in addition to carbohydrates, for energy before, during, and after workouts.
This process is best accomplished gradually. An athlete that is used to eating high-density carbohydrates regularly in their diet might be better served to start at the Lifestyle Level, limiting reliance on higher density carbs but not eliminating them all (except yams and legumes). We also know that for some people, going cold-turkey, eliminating all high density carbs except for yams and legumes not only is possible, it works quite well.
So I guess the real answer is that "it depends." How's that for definitive? :-)