Also I would not exactly say that "mobile only" "one mile only" former US speedster Mr Feelgood has exactly disgraced himself over very much longer distances here in Oz. I think he had no problems with a standing start here either. I'd be very happy indeed to have one of my mares mated with him in his first season at stud.
It's really mostly all in the training , not always in the horse's breeding or if their sire was some "one mile only" young speedy US sire. Breeding is fine but without the right trainer and handling in their careers , often it makes no difference who their sire is.