I think they were intelligent, sure. But as I said, I think brilliant has a positive connotation, where intelligent is more neutral.

Mao, Stalin, and Hitler weren't brilliant at anything except being ambitious, amoral, and rather deluded. Their only real talents were a flair for populist rhetoric and a knack for brutally eliminating and repressing political opposition using methods that morally normal people recoil from.

None was particularly effective as a military commander - which is something we should be grateful for, because if the Nazis had been ruled by someone with the military skills of Napoleon or Julius Caesar we'd all be fluent in German and xenophobia.

In fact they all did huge physical and psychological damage to their countries - something a genuinely brilliant political leader would have avoided.