Curious if we could test/compare (popluation-level) memory skills before/after writing was introduced to the population.

I want to say "I remember things better when I write them down", and because I think I'm a smart person I think my memory is good.

I don't know how well I'd remember things if I'd spent a large portion of my life building memorization skills. Maybe I could be 100x better at memory if I exercised it more?

You could theoretically do it with uncontacted tribes that don't practice writing, but in practice it'd be very very hard to establish a scenario to administer such a test, especially ethically.

Even then it would be a bad study because you'd have an extremely narrow biased sample with a very specific culture. It'd be impossible to separate out cultural or genetic differences.