Per pound of meat? That's easy: some dead cow, by far. Much worse for the environment. Massive factories are the best ways humans have found to be efficient and producing massive quantities of things. Everything else is less efficient. Inefficient means waste. Waste means bad for the environment.
Yes, we're bad at it still. Do you claim that humanity should never undertake new efforts? If you don't claim that, then you must accept that we're going to be worse at new things than things we've been doing for 10,000 years. It will get better.
Sorry, but you are wrong. Massive factories means a lot of waste. Dead cow means a lot of usable stuff. Meat, bones, skin, everything is usable. Even cow's waste can be used as a fertilizer. Massive factory? That means massive amount of mined ore and wasted energy. What does a cow need? Zero ore and some grass.
You are 100% wrong. Our meat production system essentially is a massive system of factories (aka factory farms), with tons of pollution and animal-torture along the way. Cow burps are a major source of methane (https://www.fao.org/news/story/en/item/197623/icode/) which contributes to climate change. Animal waste is used as fertilizer but we produce so much we still end up poisoning nearby land (https://foodprint.org/issues/what-happens-to-animal-waste/). Feeding cows takes a ton of energy in the form of food because you need to grow an entire cow, most of that energy just ends up wasted (cows are not big batteries).
Yes, we're bad at it still. Do you claim that humanity should never undertake new efforts? If you don't claim that, then you must accept that we're going to be worse at new things than things we've been doing for 10,000 years. It will get better.