I would say that inventing new technologies is one of the things that isn't possible when you've enslaved the inventors and made them farmworkers.

I mean, making them do research might work. That's a command economy, aka actually existing communism. Should be able to invent the waterwheel and crop rotation.

I do think it's hard to invent antibiotics and the Haber-Bosch process, and without that you are still in a Malthusian economy where everyone's going to die if they slack off farming.

Well yes, but how is this even relevant to the conversation? No one says innovation thrives with slavery. The point made is very simple, it's about commandable energy and EROI in particular. No amount of antibiotics can change that.