Altitude: Is it a Factor?

Before beginning on culture, I've taken a look at the aspect of altitude.  It is a popular belief that because the Kenyans are at such a high altitude, this causes them to be better endurance athletes.  This is somewhat backed by evidence: as the air at a higher altitude is thinner, the body produces more hemoglobin/red blood cells (in order to adapt to the decreased amount of oxygen), and it seems like this extra hemoglobin would then help an athlete down at sea level, because they would still be able to produce more oxygen (Grimes).  But the problem is, there is no undeniable proof that this is true, and the tests that have been done measuring the performance difference at sea level after high altitude training have come up with different results: some athletes have improved, others haven't (Baker & Hopkins). There is even evidence to suggest that training at high altitudes can make athletes perform worse at sea level (Baker & Hopkins).  Furthermore, many researchers also agree that the "train low, live high"  technique, in which the athlete lives at a high altitude but does their training at a low altitude, gives athletes optimal performance; this is not how Kenyan runners live (Kopytoff).
If being at high altitudes really is such a big factor in running prowess, then of course there should be many great runners from Nepal and Peru, but there aren't.  Also, the countries of Tanzania and Uganda have high altitudes and are located adjacent to Kenya, but their athletes are nowhere near as successful as the runners from Kenya (Tanser).  For example, while the Kenyan men have won the World Cross County team championships every year for the last ten years, the Tanzanian men have never even won a medal (Tanser).  Although the high altitude of Kenya may be a factor, I don't think its the biggest one, and its definitely not the only one.