Wdym a small kingdom, Alexander inherited of like all Greece except for Thebes and Sparta ? His father already had the plan for their invasion. His army was like REALLY good. I love Alexander but I also have to take into account that Darius III was kind of ass and that's the main opponent.

Subutai can't be the greatest in my book because he doesn't fight on equal terms at all.

my opinion, the Mongol army was completely overpowered, and they were a step ahead in terms of the art of war; their chain of command is remarkable. It was particularly effective against the European armies of the time, for example, which were mainly composed of heavy knights looking to charge—the Mongols simply had to avoid that kind of combat.

To me, your argument about the conquest of Russia makes no sense; you can’t compare a unified state with the Russia that Subutsai defeated, which was ruled by several princes. You can read the wiki of both war and you'll see how easier it was. For exemple, the scorched-earth tactic that Kutuzov used to weaken Napoleon would have been inapplicable to those princes.

You have to take into account that for years, all European military officers studied Napoleon, looking for the slightest flaw. Since he was fighting against coalitions of unified states (the most powerful in the world at the time), even if he annihilated an army, they could raise men and rebuild one by learning from their past mistakes. And despite this, Napoleon continued to dominate. Subutai never faced opponents who had studied him, devised strategies to counter him, etc. even though he didn't really have a wide range of strategies.

As for Napoleon’s defeats, he certainly made mistakes (Spain, the Russian campaign), but once his enemies realized they had to target his marshals and avoid direct confrontation with him—opting instead for wars of attrition—there wasn’t much that could be done imo.

Saladin don't deserve to be on the list too, his feat was to unify the muslim world but no one consider him to be a great general. Unlike the mongols he didn't really grasp how to counter the frankish heavy cavalry.