Cross-wind forces cannot be exploited if you are travelling directly downwind.

So you agree that my second quote is more apposite than the quote you provided. Hurray!

Unless you also want to say Tao said that sailboats can go faster than light.

Tao obviously intends his analysis to apply whenever Newtonian dynamics is a good approximation, so bringing relativity into it is ignoratio elenchi. You asserted that Tao said that it is impossible to sail downwind faster than the wind; in fact he offered a theoretical approach for doing exactly that.