We 100% know why airplanes of every shape and size stay aloft, and can calculate lift/drag extremely accurately based on the geometry of the plane and the airflow, in both steady state and much worse conditions. We have great approximations for steady state that make perfect sense and simplify the situation greatly and make it more understandable without simulation, even if they gloss over some details.

Where are you getting this terrible information that we don't know how flight works? Have you ever talked to literally anyone who has worked in aeronautical engineering, or even studied the basics of fluid dynamics?