Dunning kruger effect is real. Intelligent people tend to underestimate their abilities, whereas dumb people tend to overestimate them. Only the most intelligent people know that they are intelligent, in my experience. They can be humble, but they know, and the people around them know. At some point, the objective signs are impossible to miss. Imagine discussing with a severely autistic person; it's as clear as day that "something" is missing, and it's not just your ego talking. There is a similar but not identical observation I can make with the people around me; hard to verbalize what I mean without a somewhat faulty analogy. And no, I am not saying all autists are stupid. I'm saying there is a clear distinction you can observe between yourself and them, just like a truly intelligent person can observe a clear distinction between themselves and others. But all of this is unimportant, in the end.
You're misunderstanding me when you ask would it make me feel vulnerable or angry or challenged if I found someone smarter than me. There is nothing in the world that would make me happier. I would love for there to be someone smarter than me around, as long as they weren't dicks about it. You think me declaring that I'm smart comes from a place of insecurity and ego rather than objective analysis. I've nothing to prove, and I have plenty that i don't know, but I am objectively very smart in relation to others.
I do feel lonely and unchallenged in my subject area, like you say. It does make me wonder what you're hinting at, if I'm defining being smart in a hyperspecific way. But then this just becomes about semantics, I dont really care too much what word we use for it.
So when have I last let myself think someone is smarter than me? I genuinely don't remember, despite havjng thought about it since you asked me the question. Not even as a kid, I don't remember ever thinking someone is smarter than me, but probably.more because I never felt as a kid that it was important, nor did I feel the need for intellectual pursuits. Objectively, when I was a kid, there were people smarter than me around. It goes without saying.
But nothing is stopping me from seeking out people smarter than me. I have sought out people smarter than me. I'm at a University, I attend to scientific conferences across the globe all the time, I frequent "intellectual" forums and keep abreast with publications by the brightest minds that there are.. Not all of these people are frequent contacts though. Maybe I should make more of an effort to get to know them as people and appreciate them for their other qualities, and just accept that I'm on my own when it comes to intellectual pursuits.