The difference here to the regular argument of home grown players is that Triffitt is quality. Not an average interstate player (Blizzard, Edmonson, Mennie type players), but a real quality one, and he's only 21 (unlike Crosthwaite, Elliott players).
If we're looking at a young grade bowler, and a thirty-year-old state journeyman, then go the young grade quick, but in the Triffitt scenario, throw the cheque book at him.