Keep in mind that when Simplex began using delrin for its rear derailleurs in 1962, plastic was the new wonder material, not the cheap substitute it became. Plastic was cutting-edge, not lesser-grade. Initially, the entire range of Simplex derailleurs went to delrin, though the company quickly began adding metal back into the designs. During the bike boom, Simplex produced some very fine derailleurs (Super LJ) but the company was already known for the poor-performing models speced on so many lower end bikes - which is of course what the majority of boom-era bikes were. By that time, most upper-level bikes used Campagnolo, and it's what most racers associated with quality.