The question to me is not semi-syn vs full-syn but rather, why to pay the premium for the motorcraft name on your oil? I'm not shy at all about mixing syn and dino together if I want a mix for cost reduction, but it's such a small reduction these days.
Once it's in the vehicle, nobody including the vehicle knows if it's MC or not. There was once a time when the automaker brand on a product was some assurance of quality, but once the internet ramped up, this became not worth as much money as it once was.