Yes that is their model of AI risk. However the people worried about AI risk are not worried about any single organization controlling AI. They are worried about a world where no one controls AI.
Controlling AI is actually a very difficult and unsolved problem. OpenAI is not intended to solve that problem, and if anything they are making it far worse by accelerating AI research before the problem has been solved.
AI is the only thing I believe has a very high probability of destroying all humanity. Probably within our lifetimes. And there is probably something we can do about it right now - working on the control problem.
All of them are real dangers, and present dangers at that. But they still are not existential dangers. Even in the worst case humanity wouldn't go extinct. It's unlikely even modern civilization would collapse, just a few countries.
AI is one of the few things that can literally wipe out humanity, or even the entire universe. So I think it's worth special consideration. Personally I also believe it's far more likely as well. And people are already doing things about climate change and nuclear proliferation. Until very recently, there were only a few people working on AI risk, and it's still nowhere near enough.