I agree and disagree with certain aspects. There are those that work extremely hard to produce the performances and marketing/interviews that goes with it but there is also a considerable amount of luck to take into consideration. When these actors land these comic book characters which become successful, they are turned into superstars and this is mainly down to the source material and people behind the scenes all collaborating to make a great product yet its the actors who take the largest share. I understand why, they can now negotiate larger sums as people have become familiarised with the character.
With athletes they don't have the sort of luck, its just 15-20 good years of competition to be the best or being left behind. The dedication it must take to get to a superstar earning level must be impressive and you don't get there by luck. Then when these people hit 40 they usually have to retire (depending on the sport) which is a limitation many overlook. Actors can work till any age.