We can never actually run such a test but we can try the thought experiment. Even if you are one of the "greats," most of your theorems, even the best and most surprising, would have been eventually proved a few months or a few years later. Other theorems would never have been proved because no one, other than the non-existent you, would have cared. Other than speeding up science a little bit, you cannot get a long-term individual impact on the field solely by proving theorems.
But proving those theorems builds your reputation and with that reputation you can shape the direction of the field. With this reputation you can, for better or for worse, help shape the direction of the field and set the research agenda for a generation of young graduate students. You also have lasting influence through your graduate students and the undergrads you convince to study computer science.
We can run this thought experiment the other way. Suppose many years ago a sperm darted right instead of left and fertilized an egg that hatched a true genius in our field. How much difference could that one person have made on our research and our lives?