>Immersion (even for ~50min, 5 days a week) is easily the best way to learn. I don't know why anyone wastes their time with anything else.

I think once you're somewhat proficient in the language, this is true.

I'm currently taking Spanish courses in uni, and my professor is from Cuba. She's the sweetest lady, but has a tendency to ramble off in Spanish. About 50-60% of the time I can (vaguely) follow her, but the rest of the time I'm just hopelessly lost. And judging by the silence the rest of the class has a tendency for, I'm not alone.

Anyway, I'm certainly not trying to counteract your point, just to say that there are steps up to 100% immersion that I feel are necessary.