[bunderbunder]

Also the FSI estimates are for what it takes to get people who've tested into a FSI language program to that level. Individual differences are known to be a huge factor in language education, and FSI has the luxury of only needing to worry about teaching people who they know are well-suited to learning using their methods.

I doubt they're accurate at all as an absolute measure of how long a random person needs to study to reach S-3/R-3 on their aptitude scale. But based on my own experience and comparing notes with others who've studied languages from more than one of their categories, it does seem that they're at least a good indicator of relative effort. E.g, I wouldn't say that any English speaker can learn Mandarin in 2,200 hours just because that's what the FSI guideline says. But I do think it's true that the same person could learn French in about 1/4 the time it would take them to learn Mandarin.