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In that time he learned to read and write 3000 characters in context.Well actually he didn't learn them in context! That's the thing. He absolutely could not read a newspaper if by read you mean understand the content of the articles. He could mostly sound out sentences, with poor pronunciation and often using the wrong reading for various characters (e.g. pronouncing 行 as háng when it should be xíng or vice versa).
He could write many, many characters based on English keywords and pinyin associated with them in his deck. But as I've been trying to explain, words don't map one to one across languages and learning a language isn't simply a matter of memorizing words. The case of using a deck for isolated Chinese characters is even worse since a character is a syllable as opposed to a word. In modern Chinese, the vast vast majority of words are poly syllabic (i.e. multi-character compounds).
FYI, he had been studying some Chinese for a couple of years before going on the SRS craze. And he didn't take weekends off. He put even more time into study, fortunately including some things other than decontextualized SRS-based study. During the time I knew him, he largely backed off the SRS in favor of getting loads of comprehensible input in the form of media, talking to parents of his English students and his girlfriend's friends. Over time the input did lead to a better ear for the language, better pronunciation and the ability to read and actually understand. It's possible the first couple of years with the SRS gave him a good foundation that helped for the next three years of working with the language in context. I still think it would have been a better bet to focus on listening and reading from year one.