The Biological Passport can give a good picture about the assumptions of EPO. When there are clear fluctuations in the levels of Hb, Hct, Retycolocytes and Off Score, it's clear that the athlete took EPO, so it's a good instrument for catching cheaters.
I completely endorse the procedure, and agree that athletes with evident fluctuations MUST be banned, because global cheaters, looking for having advantage from any situation, and without any ethic value.
But.... this doesn't mean that ALWAYS blood manipulation can produce improvement in the performances.
The chain of improvement is very clear :
1- Athletes fear not to be able to train very hard, or to recover after very hard training
2- For that mental limit, they don't try right volume and intensity, compared with the needs for achieving top performances.
3- Somebody convinces them to take EPO, for working more and for recovering
4- With doping, they make a jump of volume and quality in training
5- The jump of quality produces better results.
The basis of the theory of blood doping is in the point n. 2 : ATHLETES DON'T IMPROVE BECAUSE THEIR TRAINING IS NOT CONNECTED WITH THE LEVEL OF PERFORMANCES THEY WANT TO REACH , and this happens because they refuse the idea that can be possible to train in that way without the external support of doping.
But the DIRECT connection with the improvement is ONLY the increase of training, and they start to increase it after taking EPO only, because before they were prisoners of their mental limits. Under that point of view, we can speak about "placebo effect", not on the performance, but for giving the convinction that is possible to train harder and faster.
This means that athletes already able to accept the idea to train with right volume and right intensity, in clean way, can achieve the same results, BECAUSE THE TRAINING IS THE REASON OF THE IMPROVEMENT, while EPO is the reason for training when athletes don't have at the beginning the mental strength and convinction for training in the right way, without external supports.
One of the external supports that can change the mental strength is their coach : a coach with very good methodological knowledge and with ethic principles, who is also an EDUCATOR for the athletes, is able to bring the athletes themselves at very hard level of training and intensity, and the results can be at the top (not depending on partuculars in training, the training phylosophy matters, not the small differences) in clean way.
Instead, when the coach doesn't have real knowledge and believes in shortcuts, or when the athlete trains alone, without coach (and among African runners this is a very common situation), the athlete look at doping in order to reach the same level of training that, before, made him worry.
At the end, I can say that we have proves EPO can enhance blood values, not that higher blood values (that are individual) can produce better results, and all the experiments made with athletes with small talent and little training can't be transported to the situation of the best in the World.