I originally thought it might just be Microsoft Flight Sim with a homebuilt cockpit
You thought right. The Flight Experience franchise offers a better product, although not by much. To their credit, just about every switch and dial is faithful to the real aeroplane - at least as far as ergonomics/position on the overhead and forward panels are concerned, but they are most definitely third-party as opposed to the original equipment spec. Furthermore, as you already mentioned, the visuals are entirely based on Microsoft Flight Sim. And for the record, I have absolutely no association with either operators.