Armstronglivs, I really doubt you understand athletics, and what regards periodization and how to train a top athlete.
1) Cheptegei has already the limits for running in Tokyo. Being Ugandan, he doesn't need to qualify through Trials like Kenyans, This means that, after a year like 2020, with WR in 5000m and 10000m and the WHMCh without specific preparation, he took a more long than usual period of recovery.
2) The current shape of Cheptegei is very far from his best shape. Probably, if he runs at his top of the moment the distances where bettered WR, is not able to run under 13' and under 27', and this has a full logic if the peak must be after 3 and half months from now.
3) Cheptegei paced from the start all the race, and was attacked in the last 200m only. While Musigala is athlete able running 3'30", and the tall, new Kenyan talent is already able to run 3'34" (if I write is because I know his training...), Joshua at the moment is still in a totally aerobic phase, and there are not yet lactic workouts.
4) The difference, for athletes of longest distances, in a race of 1500m when are in top shape for their event, and when are in the Fundamental Period, can be also around 10", before starting the period more dedicated at specific speed. For example, Shaheen (whose PB was 3'33" at the end of 2006 in a race of preparation before the two victories in the World Cup in 5000m and Steeple) in April never was able to run under 3'40" and 7'34" at sea level (and 8'15" in steeple), coming from WCC Championships and a winter with the goal to increase his Aerobic Power. In 2005, when ran 3 times under 8' and won very easy WCh in August, after the cross season (4th in short and 8th in long run in two following days in WCh on 19-20 March), almost two months later (13th of May) run 2000 steeple in 5'14"53 only, something that in August could be the passage in a race of 3000 steeple.
The problem here is that almost all the posters don't have any idea about how to train for peaking in one season, maybe because the athletic seasons in High School or NCAA are very long and it's practically impossible to have a plan for being in top shape when athletes need, since is a must for them to compete in all the race requested by their University.
Another thing : while in US there is a very good knowledge about the level of talent for sprinters, throwers and jumpers, there is very little knowledge about the talent for long distances. This is exactly the opposite ogf the situation in Kenya : there, when a sprinter is able running in 10"50 in altitude (that means 10"70 at sea level), Kenyan coaches think to have in their hands a big talent.
At the end of the day, who is not able to recognize the talent, every time speaks for doping, without any proof and any evidence, apart his "belief" that some performances can't be achieved in clean way. Nothing scientific, nothing proved, only suppositions that for long time were the reason of bad performances in the Country, creating limits that, instead, were not so difficult to overtake, with adequate training and right mentality.