As acknowledged by study, it's too simplistic to verify. Things that were not considered were: negative roll yields on volatility products; volatility tends to spike, and not gradually creep up. Also, entry/exit points - it's easy enough to pick in hindsight.
Having said that, I'm sure there are people trading it successfully. However, it would be easier to go bearish volatility during times of backwardation as these last for shorter time frames as can be seen from the urls graph.