For me the real story here is that he actually took EPO.
I've wondered if or when it was going to be used in boxing but this is the first time I've heard of a clear example of it.

It's been very common in endurance sports for many years now and the edge you gain condition stamine wise is significant.
There is a test for it now, not used in boxing, but you can still get away with it anyway since it's only detectable for a short period of time after being used.
So what you do is, use it in training where you're then able to train much longer and much harder.
That's why in track and field and cycling mainly, they have a lot of out of competition tests.

It can also, if not used correctly, which it wasn't in the beginning in cycling for an example, be a serious health risk but I think the scary thing is, when it shows up in a sport like boxing, the danger not to yourself but unlike in endurance sports, to the opponent.
In a 12 round fight both fighters are supposed to get tired and the fresher fighter will have a huge edge.

Accidently I remember the Mosley - DLH fights as pretty even and I wouldn't be suprised at all if DLH with his resources was be on performance enhancing drugs as well.