Time Diversification: Tool, Fallacy or Both?

It seems fair to conclude that time diversification is more nearly a fallacy than a tool. Total periodic returns based on random annual outcomes expose the practice of diversifying with time not only as unproductive but as extremely risky as well. Yet, as the contrived distribution of alternating returns of 30% and -10% demonstrated, it is impossible to completely reject the idea that risk can actually decrease over time