>I don't think vocab can be taught. The reason is, vocab is very highly correlated with IQ, which is stable thought life and cannot be boosted.
The fact that IQ and vocabulary are correlated across a population doesn't imply that, and it's clearly not true unless you don't think someone can learn a new language later in life. Or you think that a person can learn 10k new words in a new language, but not an extra few thousand in their existing language?
>Competent writers have a varied vocabulary which does not come across as forced
Yes competent writing requires some minimum vocabulary. It doesn't require a vocabulary sufficient to score near perfect on the SAT. Most writers limit the vocabulary they use to match their target audience, so having a much larger vocabulary than your target audience isn't going to be that useful.