I can think of a lot of caveats to this (you don't want someone in power to be half a rationalist, or a strong rationalist whose values conflict with yours), but I think the basic principle you're pointing at makes sense. Something along the lines of: "the more influence a person's decisions have, the more one wants them to have good decision making methods". (Assuming that influence means control over things that you (or the person whose perspective you take) value.)
If we're defining rationality as winning (I get the sense that's still controversial?), then the best decision making methods a human could use would be those of a strong rationalist who shares your utility function.
A couple other things you could derive from this:
I'm not sure if this has been addressed before. I think increasing your influence if you are already a strong rationalist has at least been implied, and 18,000 Hours is a specific case of it. I don't immediately recognize the version that you stated from any LessWrong articles, but Harry used that reasoning in deciding to befriend/corrupt Draco Malfoy in HP:MOR.
Would one apply this by focusing on influential people, or people who appear likely to become influential, when trying to make more rationalists?
I've read about a quarter of the sequences, but I'm not sure if this topic has been addressed on LessWrong before. If it has, let me know.
The Upward Scaling Importance of Rationality goes like this:
The more influence your thought process and decisions have, the more important it is that you're rationalist. In the grand scheme of things, it is relatively unimportant that a barback at a restaurant is a rationalist, and I say this having done that. It is extremely important that a leader of a highly influential company, or a president of a university or country is a rationalist. Their decisions affect thousands if not millions of people.
The more influential you are, the more your decisions have potential to screw over other people. Influence doesn't necessarily have to be in a management position: elementary school teachers and police officers are highly influential, even though they aren't in control of an organization. Influence can even be by virtue of the people you reach out to. A famous person with a large fanbase or a parent of a child prodigy, both have the capacity to influence the world with their decisions.
Though arguably, this can be extended to anyone who votes.
So rationality scales upward: the more influential someone is, the more important is it they're rationalists. Neglecting this can have bad consequences.