If Larry Holmes was forced to fight all mandatories and fellow belt holders ( and presumably won ) he’d make top 3
The question is hard to understand. Are you saying they could only fight the top five contenders from the start of their career? Or after they won a title? From the start of their careers, basically all fighters would be impacted. So would the top five, because they'd be fighting a bunch of guys with barely any pro fights and few wins. It would be a train wreck for all involved. If you mean after they won a title, Larry Holmes (mentioned above) is a good answer.
I guess it would have helped Marvin Hager since he wouldn’t have been allowed to fight Ray Leonard. I think the biggest impact is we’d miss a lot of important fights (and some duds for sure). This eliminates guys stepping up from one weight class to another to challenge in champion vs champion fights like Sanchez-Gomez and poor Henry Armstrong would just be a guy. It would probably have eliminated the more active champs pretty quickly … guys who were having four title fights a year would churn through top fives so quickly if they kept winning, but on the other hand they’d wear out in a year or two.
