Many computing problems require a search among an exponential number of candidate outcomes. In classical computing, a naive algorithm would consider all those candidate outcomes one-by-one, thus taking exponential computing time. Compared to such naive classical algorithms, quantum computing promises an exponential reduction in computing time, at least for some computing problems.
What if, for those or other computing problems, smart classical algorithms exist that also achieve an exponential reduction in computing time?
That is, without downplaying the potential of quantum computing, could it be that classical computing has the same potential?