Distance running takes more work, not necessarily harder work, but sub ten takes work too but unlike distance running, sprinting at very high speeds is not natural for humans it takes time to learn proper sprint form. But distance running requires you to put more hours in but typically 60-80 percent is easy mileage, it takes patience. I personally believe the 100 is more competitive and sub 10 is harder. If you look at the wind less than 80 people can actually run sub 10 without a good tailwind, even though 129 have done it .The reason I believe the 100m is more competitive is because the sprints are more popular and there are less events. Typically only 100 and 200m runners can run sub 10, but sometimes a 400m guy does it. The competition gets taken away from the 5000 by the 1500 the 3000sc the 10,000, and even the half marathon sometimes. Their is less security between the 5000 and up its all nearly 100 percent aerobic, it just requires slightly different training.
Almost all sprinters want to run the 100m, Michael Johnson said it Wayde and Norman want to move down eventually. Most distance runners want to move up eventualy to the marathon sometimes before their 5000m peak. Some even go from the 1500 to the Marathon it shows the difference in specifity. The average 100m elite can't run anywher near an elite 400m.