Are democracies more economically productive than autocracies? The book The Dictator's Handbook claims in several places that democracies are more productive than autocracies. It's central to their argument of lower taxation rate in democracies giving more wealth than higher taxation in autocracies.
They further claim that democratizing an autocratic nation will make everyone more productive, and increase wealth available in the country.
Is this true? Is it accepted among economists that democratization leads to wealth?
In economics, it is accepted that countries with good 'inclusive' institutions, such as strong property rights, are more productive and able to develop faster (or even develop at all) than countries with bad 'extractive' institutions, such as forced labor (see Acemoglu 2008, Acemoglu &amp; Robinson 2000a, 2000b, 2001, 2006, 2008; Olson 1984, Bates 1981, 1983, 1989 and sources cited therein*)
Democracies do  adopt inclusive institutions more often than dictatorships but not always (e.g. see Lindert 2004, 2009 + sources from previous paragraph). Furthermore, the ability of country to develop and become more productive and prosperous, or fall of a country in terms of prosperity and productivity may not only depend on a single institution but rather whether country predominantly has inclusive or extractive institutions (although some inclusive institutions like property rights are more important than others).
Consequently, it would be fair to say that it is accepted that democracies tend to be  more economically prosperous, but it is all conditional on the institutions they adopt. For example, a Venezuela is de jure a democracy but in indexes that measure strength of property rights it gets very low scores (e.g. see evolution of their property rights index (0-100) between 1995-2020). On the other hand consider China that is clearly a dictatorship both de jure and de facto, but their property rights index score between 1995-2020 got better.
To sum it up, given the above it would be fair to say that the view that democratization leads to better economic outcomes**  has some merit but with caveats. It is not that democracies are more productive by virtue of being democracies, it is thanks to their better (inclusive) and more robust institutions and in principle dictatorships could adopt the same institutions, but they tend not to. This is because while the extractive institutions might be bad for a country as a whole, as their name suggest, they help political leaders to extract economic resources for themselves.

* Note this research is also summarised in Acemoglu &amp; Robinson: Why Nations Fail? which is book that is written in a way that is more accessible to laymen readers than the papers mentioned above). 
 ** Meaning, among other things, government can often in the end collect more revenue even with lower tax rates because tax bases critically depend on size of output being taxed (e.g. $10\%$ tax on tax base 1,000,000€ gives government more revenue than $50\%$ tax on tax base 1,000€).