I don't think its wildly optimistic at all. Coming here, reading stuff and commenting is such a self-selecting process that it leaves you mostly with people who have extremely high cognitive function and intellectual curiosity and bravery. This is so far away from the fold and is an extremely aggressive filter.
The dread is that even this suggested "5%" contains many idiots (this idea of 5% also being rather idiotic). But if you think 5% is wildly optimistic then I fear you don't appreciate what the baseline is like. People are proper stupid and uninterested in thinking when it comes down to it.
To get a mild appreciation of the bar, at least in technical ability. My source is the OECD’s Programme for the International Assessment of Adult Competencies (PIAAC), specifically its assessment of “problem solving in technology-rich environments.”
Around 5% of the sample on average (116k) got to the top level. A top level task was as scary as being able to successfully reschedule a meeting in an email client with multiple participants. That's the sort of bar 5% can clear, which gives me the anchor. So think about that, well over 90% of people really struggle with that level of task, which I'd imagine all of us could clear (even our idiots). Sure its an annoying task, but its really not _that_ hard.
This is a website of words. The average person looks almost exclusively at moving pictures.
I'd suggest we're at least top 5% of some key things that make up intelligence: like curiosity and intellectual bravery.