Boxers who beat ATGs and former champions are always in a lose-lose situation, unless it's a passing of the torch from the elderly fighter. Has anybody else noticed how great fighters past their prime get the benefit of the doubt almost always? If they lose, they're past their prime. If they win, they get all the credit in the world. NAME some examples. Roberto Duran is one of the best ever, but he definitely benefited quite a bit from this when it came to losing against Benitez and a few others.
I don't think the Benitez loss ( Beat Duran on points in 1982 ) was a fluke, rather he had a style and speed that would always trouble Duran. Besides Duran was only 30 when it happened.
People are far too all or nothing. Instead of just taking the win of the merits of the opponent at the time, it's either a prime win, or completely worthless. Usually based more on their agenda than anything else.
I feel like you should take it on a case by case basis, and work from there. As a rule, to which there are always gonna be exceptions, I give the winner (if he's the younger guy) credit, but don't take away from the loser. For example: Ezzard Charles vs Rocky Marciano, I don't take credit away from Charles because he lost (and not just coz it's Ezz ), and I give credit to Rocky because Charles was a top three contender at the time. Even if he was way past his best, he was still one of the best in the world.