This shows when you call both Watts and Vonnegut a nihilist. Absurdism for example is not the same as nihilism.
I’m surprised how you can get a philosophy degree and then be afraid of “reinventing the wheel”. I suppose the author is self-aware enough to know what he doesn’t know… but still. It’s odd.
I don’t begrudge the author for writing it, blogging is in large part a “this is what I’m thinking about, take it as you will”, and that’s ok. Just noisy.
Technical fields have similar fundamental courses...
Nihilism's a feature of positions/schools more than some philosophical school of its own, and that feature's strongly present in much of Vonnegut's work. Existential nihilism is a key element of absurdism (which you mention)—in a philosophical sense, and in the places where that intersects with literature, not necessarily in the colloquial senses of the word.
In some areas, sure, Vonnegut's not particularly nihilistic. I don't think it'd make any sense to associate him with moral nihilism, for instance.
Watts, IDK, he's on my to-read list but it's a looooong list.