I am on the side that says the farmer didn't plow the field. I guess you could say he took responsibility for it, which isn't the same thing. I guess a counter argument that some would make is that the farmer didn't plow the field if they didn't pull the plow themselves (or to a silly level: if they didn't plow the field with their bare hands). They just pressed the right pedals while sitting in the tractor. I am not sure I have a good argument either way, but a farmer plowing a field with a tractor is physically involved during the whole process, and it feels more fair for them to say that they plowed the field, for the simple fact they weren't doing anything else during the process other than constantly controlling the plowing machinery.

What if the farmer built/tested/refined the pathing/automation around the tractor? I mean it probably doesn't ship knowing the most optimal way to plow the layout of his fields. There's still some knowledge/skill required in optimizing that portion.

The argument does eventually degrade over time, though. For example, in the future the farmer uses satellite imagery fed into an advanced AI to build the most optimal route. So yeah, eventually the farmer loses all utility I suppose beyond being a land owner (until AI owns land lol).