Attempting to prove a negative is a logical fallacy. See David Hackett Fischer's Historians' Fallacies. It is an interesting and quite useful book for anyone who wishes to do historical writing.
The case for and against Napoleon being a dictator is interesting. The first thing would be to define what a dictator is in late seventeenth and early nineteenth century Europe. It appears that the 'model' that is usually used is that of the twentieth century, and that is not only not applicable, it is somewhat ludicrous. Napoleon's government and how he ruled is available for research. And the material from those who were in his government, such as Baron Fain and Lavalette, among others, are interesting to read and study. They are essential in understanding Napoleon's government.
To bring in the idea that Napoleon wanted to conquer 'in the steps of Alexander' is nothing but pure conjecture. It also leaves out the fact that Napoleon was not the aggressor in the campaigns of 1800, 1805, 1806, 1807, and 1809. And a discussion of the campaign in Spain and against Russia gives enough 'blame' to all sides.
To bring up Metternich's 'peace' offering in 1813 is on its face somewhat tongue-in-cheek, as the proposal from Metternich in the summer armistice was a done deal-against Napoleon. Austria had already decided to join the allies and did shortly after the meeting. Prussia and Russia were on the ropes and were broke. All three nations received generous financial assistance from Britain to continue the war.
So, before attaching the 'dictator' label to Napoleon, his government should be judged against both his fellow heads of state, who were autocrats and absolute monarchs with the exception of Britain, which had a corrupt parliamentary system in place, and not by early 21st century standards largely based on British and allied propaganda of the period.