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.