There is a small problem that you don't consider : for all the athletes competing together Haile and Kenenisa in their record attempts in 10000m, there were the best pacers allowing them to reach their REAL potential. Instead, Haile and Kenenisa NEVER were helped longer than 5000m (in the case of the record in Hengelo, Haile had pacers for the first 3,200m only).
You understand that running in a group paced at the maximal individual speed (of course, related with the runned distance) or running alone, against time only, is not exactly the same thing.
In Bruxelles 2003, Haile wanted to attack his WR. I had one my athlete as pacer till 5000m (Joseph Kosgei), going till half race in 13'14". After this, Haile went directly in front, pushing the pace. Normally, after 6 or maximum 7 km at that pace he was alone, but in 2003 after 7 km he had still other 2 athletes coached by myself (Nicholas Kemboi and Ahmed Hassan, alias Albert Chepkurui) following him. Haile continued to push at a speed of 63" per lap till 8 km, when decided that couldn't risk to bring somebody else (he didn't know Nicholas Kemboi, whose previous PB was 28'19") till the end at the level of a new WR, losing a record already in his hands, and suddenly started to reduce the pace till 68" per lap, speed that he maintained for 4 laps, losing almost 20" compared with the previous pace. In the last 600m there was a great final between Haile and Nicholas (1'23" the last 600m), with Haile winner in 26'29"78 and Nicholas second in 29'30"03. You can find the final of the race in youtube, if interested. That day, without the presence of Nicholas, Haile could have run in 26'10", and probably was not as strong as in 1998.
I give you some example of differences among athletes I coached, when the long distances in track still existed, because now don't exist anymore :
Nicholas Kemboi - 13'01" / 26'30" (+ 28")
Ahmed Hassan - 12'56" / 26'38" (+ 46")
John Korir - 13'09" / 26'52" (+ 36")
Moses Mosop - 12'54" / 26'49" (+ 1'01")
Imane Merga - 12'53" / 26'48" (+1'02")
Mark Bett - 12'55" / 26'52" (+1'02")
Geoffrey Kirui - 13'16" / 26'55" (+ 23")
Titus Mbishei - 13'00" / 26'59" (+ 59")
Wilson Kiprop - 13'30" indoor / 27'01"
You can see the difference among athletes REALLY preparing 10000m in specific way (Nicholas, John Korir, Ahmed Hassan, Geoffrey Kirui) and athletes preparing 5000m, and RUNNING with that preparation 10000m (Merga, Bett, Mbishei).
Exceptions were Moses Mosop (who could run 26'30" in the period of WCh 2005 in Helsinki, but when senior never ran the distance in some meeting, apartone time in Hengelo) and Wilson Kiprop, who never ran 5000m (he was the World Champion of HM in 2010).
For your info, in his two attempts against the WR of 10000m, Kenenisa was one time sick, and the other time in very far shape from his best (that according to him was when he betterd the WR of 5000m, with an amazing "solo" after 2400m).
You can see all those competitions in youtube, and understand how much room of improvement there was, if it was possible to be helped by pacers in better way.