The dark forest was one of the most popular Fermi solutions long before Liu's books, people just didn't refer to it by that name. Take a look at Fermi paradox Wikipedia article revision history.
I don't think Dark Forest is a good explanation, though. If you were one of the first space-faring civs and meant to avoid competition by striking younger civs preemptively, you could spread von Neumann probes all over the galaxy and either keep new civs at some technology level cap or destroy all the planets right away.
Also, there is no stealth in space, so you can just send a relativistic kill missile to any worlds where civs pop up, without having to step foot outside of your home system.
I love the book, but he didn't solve the Fermi Paradox. Nor did he come up with this explanation.
If that was the question, there would be far simpler answers. Like encryption. An encrypted signal looks like noise. Or point to point communication, which is far more efficient anyway.
The Fermi paradox is also about another question. Why can't we find alien or their artifacts in the solar system? Any species that wants, could, with not much more advanced technology than we have, if it wanted to, essentially settle the entire galaxy in a few million years. von Neumann probes being one of the early ideas for how to do this. Species could do this even in the dark forest situation, but for some reason despite the universe being 13.8 billion years old, no one has bothered to. That's pretty strange!
The dark forest also isn't his invention. He invented the term, but the idea dates back at least to Greg Bear from Forge of God in 1987. He called it a "vicious jungle". Liu Cixin did state it in more game theoretic terms though.
