Why aren't rationalists more formidable? Because it takes more than rationality to be formidable. There's also intelligence, dedication, charisma, and other factors, which rationality can do little to improve. Also, formidability is subjective, and I suspect that more intelligent people are less likely to find others formidable. As for why there isn't an art of rationality, I think it's because people can be divided into two groups: those who don't think rationality is particularly important and don't see the benefits of becoming more rational, and those who see rationality as important but are already rational for the most part, and for them, additional rationality training isn't going to result in a significant improvement.