> That assumes that people actually owned the land that they were working and weren't renting it from a landlord.
No, it doesn't. Prices are influenced by elasticity of supply and elasticity of demand. Even without owning it, if suddenly there are not enough laborers to go around, the remaining laborers will be in higher demand and be able to command higher wages from the landlords, who would rather pay a higher wage than leave the land fallow and get nothing from it at all. As a software engineer you should be familiar with this phenomenon, even when you work without owning shares of your employer.
You are commenting on both medieval history and economics without benefit of so much as a freshman level introduction to either. The rest of your post is full of similar misunderstandings and disputing it point by point would be tiresome
The main point you're missing though is this: Yes, allocating the profits between capital and labor (as between land and labor in ancient times) is a perennial war. But unlike then, now the pie actually gets bigger. There was no way to make more land before, other than to conquer, discover, colonize someone else's. Fundamentally zero sum. But today, creating more capital actually creates more "fields that can be worked" thus increasing demand for labor.
In times of secular stagnation, it does seem, to the chagrin of myself and anyone else who isn't already independently wealthy, that labor always slowly loses gains in a relative sense. But any time things start changing or expanding again, the "Lord would rather have peasants at a high price than a fallow field" effect always starts helping again. And in either time, the vast amounts of capital created (by which I include physical plant, invented processes and technologies, and even acquired education and skills inside of the head and belonging to laborers) help everyone get richer. This is why the poorest in America often have access to air conditioning, antibiotics, and cell phones, unheard of luxuries at one time, even when they are unfortunate enough to live in a time when the big rentseekers slowly chip away at their percentage of the profits.