Training hard and training heavy are two differenct properties. A powerlifter with a 600 lbs bench won't be training hard if he benches 300 lbs for 10, but for a much weaker man, doing even 6 reps with that weight will be exerting a much more brutal effort than it is for the powerlifter to do that weight for 10.
Dorian trained harder because he often used weights that pushed the limits of his strengh, and he took sets to failure. Dorian would do usually 6 to 8 reps per set, and he would choose weights that were heavy enough for him to fail after that number of reps.
Ronnie, conversely, would use weights far beneath his strengh, evident by the fact that he usually did between 12 and 15 reps per set, and even by the 15th reps he didn't achieve failure yet. This suggests that he usually trained with weights that were 50% of his 1RM, while Dorian trained with weights that were 80% of his 1RM. The only time when Ronnie trained harder than Dorian was when he did those insane doubles on the deadlift with 805 lbs or squated 800 lbs for a double. The problem is that this is not how Ronnie often trained. Dorian definitely trained harder, but the title of strongest Mr.Olympia definitely goes to Ronnie.
