As it is well-known, Komodo dragons today prey mainly on deer, water buffalo, pigs, goats and horses as adults. However, these have only been present in their range for 4-5,000 years at most. And even ignoring the fact that the idea that Komodo dragons evolved gigantism to prey on pygmy stegodons is disproven (though they likely preyed on them anyway, they were already giant when they reached Indonesia), the pygmy stegodons lived during the Middle Pleistocene, meaning there were hundreds of thousands of years between the extinction of the pygmy stegodons and the introduction of mammalian megafauna by humans. So, what were Komodo dragons eating between those times? I think I heard David Attenborough say in a documentary that they cannibalized younger members of their species, but living on this alone violates the laws of thermodynamics.