Bhasin's study is fundamentally flawed in that it sampled muscle size while they would still have inflated muscle size from increased glycogen and water retention from the steroid use and didn't use a method of measurement that compensates for it. It is not a direct comparison of contractile tissue, which is presumably what we would care about.
Belgian Blues grow that large because of a mutation with their myostatin gene. This is hardly the same method of action.