This is really cool. I agree with your point that a human would also struggle to book a flight for someone but what I take from that is conversation is not the best interface for picking flights. I am not really sure how you beat a list of available flights + filters. There are a lot of criteria: total fight time, price, number of stops, length of layover, airline, which airport if your destination is served by multiple airports. I couldn't really communicate to anyone how I weigh those and it shifts over time.