> Why do you keep harping on Mandarin in particular?

The original claim was about 20 Mandarin words.

> The learner already knew how to spell "light" and "house" so it was effortless to learn "lighthouse."

This kind of comparison doesn't work properly for learning Chinese characters. Simply combining characters like that only works ~half of the time or less.

> EdIT: One hour a day devoted to language study will yield 20 new vocab words a day that, over time, you'll have around 85% recall, which translates to over 6,000 new words per year (over 7,000 but then you adjust downward because of the 85% factor).

Delusional for Mandarin, unless you have some kind of special brain putting you in some 0.001% of the population. Not even natives learn that many words in a year. That many characters they might know when reaching university, and then later forget many again. Most native adults don't know that many.

> The issue is that people want to learn a language in five minutes a day, but they don't bat an eye at playing a video game an hour a day to be able to beat some level. I remember playing for hours to be able to get good at 1942 on the NES back in the early 90s.

Well, at least on that we agree. If one doesn't put in the time and effort, then the results will reflect that.