Nobody is disputing this. You can, however, clearly be more or less 'rational', adopt better or worse heuristics, etc. which is what you attempt to get from reading LessWrong or Kahneman.
But what constitutes a better heuristic is context dependent. In particular, if I must make a decision in a time-constrained manner then any heuristic that blows the time budget is going to be worse even if it would be better given more time. And one can't really know in advance how much time spent thinking is optimal. So one has to pick a strategy. The fact that humans have evolved to use a variety of strategies fast and slow (depending on the human) suggests that there is no single optimal strategy.
Sure, but I doubt you actually think that everyone is already operating as well as they can within the contexts they are placed. There's definitely room for improvement. There are all sorts of scenarios where even knowing nearly optimal techniques outcomes can be improved by going the TimSort way due to the context you most often find yourself in.
