is Duran overrated as a lightweight? quality of opposition?

This is a ridiculous remark.

There are numerous examples of revisionism which is now widely accepted as the preferred version.

Best, probably, is the notion that World War 1 officers in the Allied ranks were "donkeys", birthed from the popular phrase "lions led by donkeys" perhaps coined nowhere better than in Alan Clark's "The Donkeys", a book which sculpted thinking on the trenches in WW1 for two generations - more recently, this point of view has been debunked, to a degree, by revision of the history of WW1 combat. Combat officers get a far, far better break than they did in the 60s and 70s.

Kl, the masterpiece by Nikolaus Wachsmann, has completely revised how the birth of Nazi concentration camps occurred and retells aspects of Nazi targeting in the early days of the camps; for the most part this has been successful. Now the definitive text on the matter it was written nearly 80 years after those events began.

If you prefer an example from boxing, take Harry Greb. A womaniser and an alcoholic for the best part of a century, his reputation was revised by work done by Bill Paxton and Steve Compton.

Columbus was America's hero for decades; now he is regarded as something of a tyrant, a murderer, and perhaps not the man who discovered America anyway. This is still in question - it is currently being revised.

History is never finished - ever. There is always new data, new points of view as society evolves. Christ, we don't even know how many fights Jack Johnson had for sure and he was the heavyweight champion of the world. Archie Moore, Koichi Wajima, Bert Lytell, Jimmy Wilde, their records are likely incomplete and new data could arrive any day.

Just because someone says something for a long time, it absolutely does not make it true. History is constantly - constantly - being revised, in it is in absolutely no way the enemy of established history. The idea that "the truth" is a frozen perspective for anything that happened in the past has been proven to be untrue literally thousands of times.