A good question that can easily be answered, Tsyzu fought and beat a former world champion in only his 4th fight! Nearly 50% of all the fights he has had as a professional have been against World Champions.
He was the undisputed 140lb champion and universally recognized as the best 140lb fighter in the world for 10 years. Interseting that both former lightwieght Champions Mosely and Mayweather chose to avoid Tszyu like the plague when they both had a chance to move up and fight him.
De la Hoya didn't stick around to long in the 140lb division either for that matter.
His loss to Hatton is no black mark, age catches up with all fighters, do we question Duran, Leonard, Chavez or Hearns who all lost to fighters who wouldn't have lasted 5 rounds in their prime.
Tszyu's record stands up allright, have another look at how he demolished Gonzalez, Judah and Mitchell.