"All things being equal, if we could simulate the same scenario, he has a lot more difficult task. He's elected to swim six individual events, as opposed to what I elected to do, which was four"

Mark Spitz is referring to the trouble of his own job compared to someone else's. He is stating that if all other elements are equivalent, the other person has a harder task due to the fact that they have actually chosen to swim 6 individual occasions, while he just chose to swim 4. This suggests that the other person is taking on a greater challenge, and that it is more difficult to swim six individual occasions than 4. Mark Spitz is highlighting the difficulty of the other individual's job, and is most likely applauding them for taking on such a challenge. He is also most likely emphasizing the significance of setting objectives and pressing yourself to attain them, no matter how tough they may be.