seeing that wasnt his routine to get big, it was only his precontest, i see nothing wrong with it. he found what he needed to perfect his body, and he did just that. he had the greatest body of his time, a true legend and icon of the bodybuilding world.
found this within an article on hypertrophe, seems to suggest that high volume is not best for gaining muscle - will still try the Arnold workout for cutting though:
Higher volume training (Sale et al., 1990; MacDougall et al., 1979) does not seem to be the best way to trigger efficient muscle growth in comparison to lower volume modes. Greater fiber hypertrophy occurs when training protocols use 30 - 40 repetitions per muscle group performed at an intensity of 75%-85% of maximal strength (Kuno, Katsuto, Akisada, Anno, & Matsumoto, 1990; Staron et al., 1989). Lower intensities (below 60%) and lower volumes do not result in as much, if any, significant muscle hypertrophy (Dons et al., 1979; Lüthi et al., 1986). Exercise performed at higher intensities with similar volumes also do not cause much muscle growth (Ratzin Jackson, Dickinson, & Ringel, 1990). In fact, experienced bodybuilders did not show significant muscle hypertrophy when they were following a typical high volume training routine (Alway et al., 1992). In comparison, those who begin resistance training do show significant hypertrophy following such a regime. This would suggest that a potential muscular adaptation to the stress of high volume weight training may occur.