Zoonotic diseases require frequent contact with large amounts of animals with large amounts of workers to have enough opportunity to make the difficult cross-species jump, so yes, factory farming is 100% the problem and giving both the animals and the people caring for them more space and making sure the workers have the time to do things right would make a huge difference. You're making a reducto ad absurdum argument by intentionally using absurd quantities and time periods that are not required to accomplish this goal.

I'm no vegan by far, but I'll definitely grant them that the modern animal product industry is unsustainable on numerous levels. Also whether or not humans are "meant" to eat meat, we're definitely not supposed to eat this much. There are aspects of other agriculture that are similarly so, however. A good example is produce such as avocados and citrus fruits that require a tropical climate but that spoil relatively easily meaning they have to be quickly transported to other areas to be consumed. They should be a relatively rarely eaten delicacy in places they don't normally grow, not something you can just pick out of a giant pile at the supermarket.

Plastics in general are another great example. You can't make a biodegradable anything that does what plastic does because not being biodegradable is exactly what makes plastics so useful to the modern lifestyle. They mean you can package something in a way that will stay sealed and fresh through all kinds of temperature and humidity changes when especially moisture is exactly what you need a biodegradable material to respond to. Plastics mean you can get exactly the flavor of doritos you're craving from the gas station at 2am. Plastics = convenience and that's the one thing that will be the hardest for all of us to give up.

Saving the planet and treating other humans better is just going to require a radical change in (particularly) western culture where we're used to just getting whatever we want whenever we want, and while the rich are certainly the most egregious offenders, one of the biggest ways they've suckered the rest of us into going along with it is by getting us addicted to small-scale versions of their unsustainable consumption habits.