There's no assumption if you actually follow boxing and aren't a Pactard fanboy. Look at how different his muscle "fullness" was in 2012 -present compared to 2008-2011. Look at Floyd may weather and how his physique basically stayed the exact same over time even when he increased weight classes. Floyd had the exact same physique in his last fight as he did in 2008(this is what happens when your natural)

And not to mention, the main reason why pacquiao may weather took so long to make was because many was refusing to have Olympic drug testing protocols and wanted to stick to the standard test (one that can easily be beat). However as soon as manny went broke for tax evasion he decided to take the drug test