Is the question (a) whether it is better to support "humane" farms than to support typical factory farms, or (b) whether it is better to support "humane" animal farms than to support the creation of plant-based or other animal-free foods?

Based on my experience working on animal welfare issues, I would say (a) it is generally better to support farms that have improved animal welfare rather than to support typical factory farms, but (b) it's still probably best to support creating plant-based or animal-free foods, since life on any factory farm still stinks.

A note of caution and clarification about terminology: The word "humane," and the concept of humane meat, eggs, or dairy, are very broad, and can have multiple meanings. That's why I tried to rephrase the question to talk about farms that treat their animals better than typical factory farms, versus farms that don't. I didn't read the book, and without context, I'm not sure what someone means by "humane." Here's why:

Sometimes food sold as "humane" is just normal factory farmed food. Sometimes, in other words, the term is a trick. In a practice that animal welfare advocates call "humane washing," a company sells products made at a typical factory farm, but markets the products in a way that tricks consumers into thinking the animals were treated better than they really were. An example of this would be if you were to see the word "cage-free" written on chicken meat. All chickens raised for meat are kept in cage-free factory farms. (The chickens who are forced to live in cages are the ones used to produce eggs, not the ones used to produce meat.) So talking about "cage-free" chicken meat would be deceptive humane washing. "Cage-free" chicken meat would be no better than any other chicken meat. Another example would probably be any package that literally says "humane" on it. My understanding is that a lot of companies think the word "humane" is so vague that they can get away with using it even when the animals in their factories aren't treated any better than animals in typical factory farms. For example, California used to advertise that its milk came from "happy" cows, even though there was no factual basis for that. 

But there are some factory farms that actually do treat their animals a little better than other factory farms. For instance, if you were to see an egg package that said "cage-free," the birds used to make those eggs were treated a little less cruelly than the birds used to make eggs that don't bare the "cage-free" label. Because instead of being kept in tiny battery cages so small that they can't even spread their wings, the birds used to make cage-free eggs can walk around a little bit. That said, they're still kept in crowded factory farms. This is just one of many examples of how companies sometimes actually tell the truth about treating their animals a little better than other companies. Other examples would be "crate-free pork," or a "global animal partnership certification."

If you are trying to figure out whether certain products are actually more humane than typical factory farmed products or not, I'd recommend looking up any claims used at this website: https://awionline.org/content/consumers-guide-food-labels-and-animal-welfare, or other similar websites put out by animal advocates. For instance, that website explains that food labeled "global animal partnership" step 4, 5, or 5+ is generally more humanely raised than other food. But it explains that food labeled "humanely raised" isn't.

So in my opinion, the question is too complicated to give a simple answer to. But if I had to summarize, I'd say (a) it is possible for factory farms to improve the lives of their animals, and that is a good thing, but (b) it would be better for animals if there were no more factory farms at all.