I just threw an approximate guess of 2-3k years. If it's 6k, more to my reasoning: there's been so much time and effort to learn those that proper principles are now well known and can be taught and applied repeatedly, reliably, affordably.
I don't think people have changed at all, and I didn't say it anywhere above, so I don't understand why you assume I think people have changed significantly.
Our knowledge in a few areas has grown significantly though (read: crafts, science and technology). I don't think anyone reasonable would disagree, but who knows.
