I also think you can't compare Rupp to Bekele, Geb, Komen, and Tergat. Those guys are historically ridiculous. I would call them outliers but since there are 4 of them, that might be too many to qualify.
In 4 years Geb took the world record from 12:58.39 to 12:39.36 in the 5,000, a whopping 19 seconds. 19 seconds! Aside from Bekele and Komen, no one else has come closer than 7 seconds to 12:39.
10,000 - the record was 26:52.52 before Geb. 4 years later, he'd dropped it almost 30 seconds to 26:22.75. 30 seconds in 4 years! No one besides Bekele, Geb, or Tergat has broken 26:30, which is still 13 seconds slower than Bekele's WR.
Something happened in the mid-90's. Drugs, super secret training, the rise of Ethipia, who knows. But the above 4 guys were/are a level beyond the rest of the world. You can't compare Rupp to them, you need to compare him to whoever is 5th best after those 4.
Pre didn't have to compete against such supermen. Keep that in mind.