Disagree. Strongly. The global economic impacts alone will severely impact the US. That's not as sexy a thing to prep for, but it's much more likely. (And both are extremely low probabilities, just more likely in comparison to an exchange with the US)
Nobody can prep for everything. Everyone has limited time and limited resources. You have to draw the line at something, but logically you should spend your resources on high probability/high risk/high reward situations first. If you want to prep for nuclear exchanges, meteor strikes, and alien invasions that's your business. Just ask if you've prepped for more likely life altering/ending events, say a massive bleed from a car crash, with the same assiduousness first.
This^
Just pitching one nuke by Russia into Ukraine will shut down the world by fear alone. Assuming no other nukes fired it will still take a long time for everything to recover from just the fear of an exchange assuming leadership can find some way of smoothing things over. Ordinary preps will help Americans through this type of crisis, everybody else will be scared and running for the hills.