Pol Pot has a curious distinction on that list. For better or worse (hint: worse), the other three leaders on that list strengthened and united their countries, all three of which were in chaotic states of distress before their leaders arrived, and made them a force to be reckoned with on the international stage. Pol Pot, on the other hand, destroyed his own country to the point where even VIETNAM said "enough is enough." Pol Pot stands with Enver Hoxha and a few others as leaders who (intentionally?) sabotaged their own countries and ran them into the ground.
Vietnam dislike Pol Pot because he was allied with the Chinese, which in turn was partially due to border disputes between Vietnam and Cambodia. Also, Pol Pot's rise to power was facilitated by the destruction of Cambodian society as part of the broader war in Southeast Asia, and in this sense he is similar to the other three, all of whom rose to power as the result of a war (although in Hitler's case, it was separated by 15 years, the cause and effect is quite clear).
Otherwise, agreed.
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