I also think Sergio had the edge in 1972. It was close, but Sergio, who was 31 that year, was at his all time best, while Arnold, at only 25, was still developing.
Arnold was far better in 1973 and 74 and would've beaten the Sergio of even 1972, but sadly they never went toe to toe after 1972.
Anyway, just a little superimposition to compre the relaxed stance of the two guys.