That's just one of gazillions of examples of guys that medaled in the Olympics and had great success in the am's but flopped badly when they hit the "world level" in the pros or even before they got to that point.
Another example...Jorge Luis Gonzalez, who probably has the best amateur resume of all-time, when it comes to the quality of names he's beaten...on his resume, two future undisputed champs (Lennox & Bowe) 3 olympic gold medalists (Lennox, Stevenson & Biggs) and four Olympic medalists overall...but as soon as stepped up to the elite level in the pros against Bowe, he got exposed badly and was made to look like a low grade club fighter...and he went into that fight undefeated with a 95% KO ratio and was tagged by the boxing press as an "avoided fighter".