[brigandish]

> I got to fluency in Japanese in roughly 6 months to 1 year while living there

Your experience is not the norm, not according to research and not according to most people who've tried learning Japanese. Either you have a talent or you had a more effective method for learning, but it does undermine your judgement as something generalisable to others.

Let's hope it's the method and you share it.

[psychoslave]

While the short time is indeed impressive compared to median learning curve, how much studies can afford a panel of people going through similar conditions of volontary complete immersion over such an extended period?