I have a problem with the weigh-in rules, but I don't blame them on the fighters provided they make the weight fairly.

Some fighters have the ability and styles (and talent) to move up in weight and be successful.

DLH was big at the lighter weights, and had the skills and talent to be successful at the higher weights. He wasn't as powerful in the higher weights, but has always had that great left jab, left hook, solid fundamentals, etc...

Mayweather is another guy who was successful in numerous weight classes due to skills, style, and talent. Yes, Baldomir is slow as molasses, but he outweighed PBF by a dozen lbs on fight night. DLH had quite a size advantage on PBF as well.

Others who rely more on strength are less likely to be as successful in different weight classes.

It also shows how special Duran and Chavez were to be successful in different weight classes with pressure styles, and how they had other tricks in the bag other than being strong and tough. They had smarts and terrific skills.