Could you say more about said research?

It's basically as above. Traits like IQ offer remarkable predictive power; Big Five on top of IQ allows more prediction, and the second paper's Small 100 seems like it'd add nontrivial data if anyone runs it on a suitable database to establish what each trait does. Much of the remaining variation can be traced to the environment, which obviously doesn't help in establishing that human personalities are extremely rich & complex.

Long-term memory is much smaller than most would guess when talking about 'galaxies of galaxies of neurons', and autobiographical memory is famously malleable and more symbolic than sensory. (Like dreams: they seem lifelike detailed and amazing computational feats, but if you try to actually test the detail, like read a book in your dream, you'll usually fail.) Skills don't involve very much personality, either, since there are so many ways to be a bad amateur and so few to be an expert (consider how few items it takes to make a decent expert system - not millions and billions!) and are measurable anyway.

More generally, people tend to think that they do things for complex and subtle reasons, while outsiders see them doing things for few reasons and transparent self-serving ones at that, IIRC; why do we believe the Inside view that we're so very complex and unique special snowflakes, while ignoring our Outside view that everyone else seems to be fairly simple?

(More personally, I have more than once had the experience of reading something, composing a comment in my head, and going to make a comment - only to see that a past me had already posted that exact same comment. This is not conducive to thinking of myself as a complex unpredictable person, as opposed to a fairly simple predictable set of mechanisms.)

If you know of any essays or papers arguing something like the above but more rigorously, I'd appreciate pointers.