The evidence in E African and US distance running simply isn't there. You're just guessing, connecting the dots, whatever. Which is fun, but it's not a great way to describe the world as it is.
The show-me-the-positives attitude was what led many people (including myself) to defend Lance Armstrong and US Postal throughout those TdF wins. Everyone knew there were dopers at the time, but it was viewed as a "European problem". Lance had special physiology...toughness...better work ethic...could beat the rest without doping. Sound familiar?
Lance Armstrong was not some outlier who ruined the reputation of his sport. His case revealed the true nature of doping professional sports. In particular: when the financial incentives are high, there IS pressure to dope, NO ONE is completely immune to this, and an athlete CAN evade detection. The pressure may come from managers/coaches, or it could be greed on the part of the athlete, or it could just be the athlete feels they must dope to remain competitive with other suspected dopers.
The testing evidence shows that most athletes stay clean. But some are not, and I see no reason to doubt that *some* of the "A-listers" are actually B-listers on drugs. It's happening. The arguments against this are weak and ad hoc. For example, the claim that someone with "special physiology" would not benefit from drugs (which does not even speak to whether the athlete is actually taking drugs) or the claim that a B-lister somehow can never become an A-lister by using drugs, or the idea that some groups of professional athletes are morally incorruptible (as if they could not see or do not care about the financial gain from running faster / extending a career), or my favorite, the idea that some super-elite athletes are too focused on training to understand what pills/injections they are taking (absolving them from responsibility?).
Another thing about "lack of evidence". What if the athlete is just not being tested? In this regard, the US and E Africa are very different. There are many out-of-competition tests performed in the US. In E Africa, not so much. It's a situation where we simply don't know what is going on. My default position in this case is "anything that can happen, will happen".