I think the main thing veganism and vegetarianism have done in recent years is win over minds. As opposed to the clichéd vegan that will mention that fact whenever they can, the number of quiet vegetarians and vegans around me has skyrocketed in recent years. Even though they hardly ever discuss it, the fact that more and more people around me, even though still a minority, refuse meat and/or dairy products for themselves has really denormalised the role of meat in our society.
And that, in turn, makes even meat eaters more likely to consider voting for a political party that will restrict industrial farming practices, or to consider eating meat from farms like the authors'. And in that sense, it might still be the answer, regardless of the effectiveness of the veganism/vegetarianism itself.
I recently started reducing my meat consumption, and I was surprised by how many people are doing the same without making a big deal out of it. That is the sort of change that sticks.
And that, in turn, makes even meat eaters more likely to consider voting for a political party that will restrict industrial farming practices, or to consider eating meat from farms like the authors'. And in that sense, it might still be the answer, regardless of the effectiveness of the veganism/vegetarianism itself.