I feel like the pendulum has swing too far in the other direction on this topic, actually. Yes people in the past weren't dumb, and shouldn't be under-estimated, but even a normal person could provide huge gains to any pre-modern society. Their understanding of mathematics, biology, evolution, medicine, astronomy, economics, reading+writing, organization, etc. are immeasurably valuable. I don't think people appreciate how much "ideas" are, in some sense, a kind of technology in themselves. Yes you probably couldn't make yourself a queen of the land with your advanced knowledge, but you could massively improve this society in fundamental ways. Like get infected with cowpox if you want to get vaccinated (a term meaning of or from cows btw!) against small pox.

>It's likely that ancient humans were adept at many of these things, like salt preservation, warm clothing, contraception, spun fibers, and boats. Many of the others (agriculture, wheels, etc) simply wouldn't make sense outside their native cultural contexts.

For people this primitive, even elementary metalworking would be revolutionary. Yes you'd have to do a bit of tinkering to work out the kinks, but iron ore pre-modern-extraction was everywhere, and once you have the foreknowledge that heat special rock -> smash into shape -> better-than-rock tool it's not hard to figure your way to something groundbreaking.

I do think you'd be limited in how much you could change things by how far back you go, but mostly due to human life span. The more new technologies you need to personally 'invent' the longer this stuff takes, as you'd need to experiment with on-the-ground resources and techniques until you can successfully realize your conceptual understanding. I know what a blast furnace is, and because I have the key concepts I can eventually build one with some trial and error. But it would take years if I had to start from just sticks and sand.