Yes, we've learned a lot in the short modern aviation era, but we're nowhere near the point where no model wind tunnel testing is required, or designing an advanced aircraft is just a matter of feeding your requirement into the computer without the need for much prototype testing, or any designer, especially those with the pumped-up ego, can just say I knew of and has completely analyzed an aircraft's aerodynamics anytime a new advanced aircraft comes into the scene. Two aircrafts may share the same basic designs, for example F-15 and the Flanker, but they're also very different aerodynamically in the details.
Yeah, more like they wouldn't have so much problem if they knew of the aerodynamics design contradiction during the early design stage, or maybe their predicted compromises turn out much worse than they've predicted. This is another proof that no designer can claim that he completely understands an aircraft aerodynamics because we've done aerodynamic studies of every possible shapes, control surfaces, aircraft configurations, and their every possible variations thereof.
