I feel like a simpler explanation is that the author is roughly average in most traits, and comparing themselves to others who are above average in certain traits.

I doubt it's about thinking speed. At times I've thought I was fundamentally deficient in some way, only to realize later that I was catastrophising about a poor performance in something and generalizing that across my entire life.

There is also a lot of variation in our abilities, mostly due to practice. When I've holed myself up in my room working for weeks I lose the ability to socialize in general, let alone make witty comebacks. But once I'm in a social environment for a while I can banter with anybody.

Practice helps of course, but arguing against differences in thinking speed is like arguing against differences in intelligence, or even running speed.