That is absolutely true, but it remains to be seen if those attempts will hold up in the long run. There is a big difference between American power being in decline (but still dominant) and the world being multipolar. I would say that currently the derivative is <0 but American power is still vastly greater than any other country.
Of course the Chinese nuclear arsenal is enough in absolute terms to destroy a large segment of the US population (and an even greater share of GDP) but I would not say the same in practice. Contrary to the US and Russia, China has a “no first use” nuclear weapons doctrine. This piece of policy does have material consequences, meaning that the PRC’s nuclear arsenal is really just a large stockpile of weapons, not a 24/7/365 array of ICBM bunkers. There is no such thing as a Chinese “red button”, but there is an American one. The PRC also possesses no significant SLBM potential, meaning that the US could probably wipe out much of the Chinese land based capability and population centers with minimal losses in return.
My intuitive feeling is that this makes too many unscientific assumptions that it does concretely support. The main issue I have is the dismissal of the techniques to kill off humanity. While it is true that it is by definition impossible to try to reason as a superhuman entity it is still the case that a rogue AI would only have a limited set of tools to try and cause a mass extinction. Wouldn’t the first step be to cite a counterexample strategy that an AI could use?
I fail to see exactly where this is argued above, loss of control does not make wiping Earth of humanity easier with nukes, but it also moves the goalpost. RAND has deliberately chosen a limited scope that focuses on extinction level techniques, and I don’t think that they are trying to offer any comfort on the horrors of nuclear war.
While I am critical of the applicability of AI research on robotics, I agree that RAND’s assumption that robots need much more development to be used for spreading pathogens is probably wrong. It is likely that drone technology has already achieved such a level, and that an advanced AI could control a global swarm of them—either directly or through human actors—to spread disease together with some sort of supply-chain attack.