Im no pilot but if they used the Blade engine to help develop the Cirrus jet (a real world AC) there must be some truth to the phyics in the sim....
Oh no doubt, X-Plane simulates airflow very well, its not completely infeasible to just skip the million dollar worth of wind tunnel tests and just run it through X-Plane for less than a fraction of the cost...
...one thing that I do like about the sim is the simulated airflow around the aircraft. Stalls behaviors, or in fact, aerodynamics are distinctively better than flight sim. (I have yet to see any FS designer that simulates the drag caused by the flat face of the compressor fans at low air speeds...or better yet, the radiator on the P-40; and X-Plane does it automatically.)
...but the model has to be absolutely perfect, a 32 sided polygon fuselage would have noticeably different aerodynamics from a blended fuselage.
Plus, I have yet to see a single aircraft in X-Plane with realistic power and weight. The most extreme example, go search for all the videos with 777's landing on carriers in X-Plane...unless Goodyear has a major breakthrough in brake pads in the near future, that ain't gonna happen.