I don't think the author, or anyone who eats meat (and is intellectually honest and invested in environmental impact), is trying to argue that it's not expensive. But if you've already made the ethical choice that you still want to eat meat, it's worthwhile to study what methods for producing it are less impactful and more sustainable.
Factory farming animals is specifically mentioned in the article as causing less environmental damage than organic or cage free methods. Whether true or not doesn’t prevent effective environmentalism from becoming as performative as environmentalism.
Which only looks at greenhouse gas emissions (and only then compares grass feeding to grain feeding), and does NOT consider the effects to local groundwater, surface water, or air quality from CAFOs.
Besides things like frequent manure spills that pollute surface and groundwater, children living near these CAFOs have elevated rates of asthma.
The piece is very focused on greenhouse gases and the benefits of "economies of scale" but doesn't say a peep about the meltdown of our consolidated food supply when the pandemic subjected it to supply shocks.