While good and illustrative, that page is based on the very restrictive view, that of choosing only one candidate. This applies to presidential elections, sure. There can be only one president.
But most countries don't have one-member sized voting districts in their parliament elections, rather they choose 10 to 30 members per voting district.
The Dictator's Handbook by Bruce Bueno de Mesquita and Alistair Smith is about just this issue, and if you want a more theoretical take (along with a detailed model) try The Logic of Political Survival by the same writers.
Plurality voting is a lot better than not having a democracy; imho at least the worst candidate will be excluded. My understanding is also that democracies of any form (including republics) tend to get much better military results than dictatorships, but I don't have any actual evidence to cite :(.
[1] http://zesty.ca/voting/sim/