Land use would be lower if we reduced livestock, but likely not massively. Lots of grazing land isn’t suitable for farming, letting it go wild would also require a massive effort to reintroduce natural grazing animals, which would likely need active management.

16% of the current farmland gives us around 75% of our diets. That means we only need around 21% for a 100% plant based diet. This also means we can free up 75% of animal land. I sure we can easily find that 5% in that whole 80%, don’t you think?

There’s also the fact most of our crops would need to change to optimize for human consumption, and humans aren’t as efficient at consuming those calories as livestock.

This is incorrect.

There’s a few diseases and allergies though where this becomes a thing. But even in such cases meat can be avoided.

Even after transitioning crops there’s going to be a significant amount that isn’t processable by humans that would sustain some amount of livestock.

This could be an argument if it was forced overnight but that would never happen. Transitioning towards a plant based society is not something that can happen overnight and will definitely take time. Phasing it out happens naturally.