My point was that it seems to me that people try to treat SOs as if they're the only one on the planet for them, which clearly isn't true.

But I agree, in a practical sense, the amount of potential SOs is definitely limited by those factors. For most people, I still think that there's enough of them where most people would find one in a reasonable amount of time. But for people with more particular tastes, it could definitely be the case that you've found someone who you're pretty unlikely to ever find someone like again.