Q. Evidence shows that in practice …

If we make a survey of  all democracies and all dictatorships for the last fifty years between 1950 and 2000,we see that  dictatorships have slightly higher rate of economic growth.  Economic development depends on factors like  country’s population size, political atmosphere, global situation, cooperation from other countries, economic policies adopted by the country, etc.
However, the difference in the rates of economic development between less developed countries with dictatorships and democracies is almost negligible. Overall, it cannot be said that democracy is sure to bring economic development. But we can expect democracy will not lag behind dictatorship in this aspect.
 But , it is better to prefer democracy over dictatorship as it provides more positive outcomes than dictatorship.
In dictatorship Saudi Arabia there is economic progress and it is a rich country compared to a democracy like India. But there is no political freedom and voting rights. In India we have political freedom,voting rights and right to express our opinion.Hence, democracy can be preferred over dictatorship.