In most sports, like tennis or golf or whatever, you compete on equal terms with every other competitor in the world. In F1, you compete on equal terms with one person, your teammate. How many other sports turn up results like this:
2015 F1 Driver's World Championship:
1. Mercedes
2. Mercedes
3. Ferrari
4. Ferrari
5. Williams
6. Williams
7. Red Bull
8. Red Bull
9. Force India
10. Force India
This is why you cannot compare Vettel, Hamilton, and the rest of them with other sporting greats like Federer, or whoever.
Football and loads of other team sports. Ronaldo doesn't compete on equal terms with anyone.