If not, why?
It depends on what you're looking for. "Wild Fermentation" has both fermentation lore and traditional recipes. "The Art of Fermentation" is heavy on the lore and light on recipes. Not that you won't be able to start a bunch of projects using this book, but there are no recipes that list exact amounts. Katz said his goal in "Art" was to help readers understand the process of fermentation so that they could just riff on their own and not need recipes.
So if you only want one, "Art" is definitely more comprehensive. But if you want some hand holding in terms of precise recipe measurements, you should get "Wild Fermentation."
I don't think so at all. I use Wild Fermentation regularly for its straightforward recipes, and the Art of Fermentation is more in-depth but less recipe driven. For the fermentation enthusiast, I think both books are helpful. When I want to try something new, I look it up in The Art of Fermentation to get some background and an overview, then I look up a recipe in Wild Fermentation.
Thank you! That's what I needed to know. I think I'll get Wild Fermentation to start with.