That was supposed to be the best undisputed fight if Casimero had been able to meet the weigh-in requirements. I think his team was unaware that they were violating the rules, so it's not that he didn't make the weight requirement - he was disqualified, which gave Butler the opportunity to get the belt against a weaker opponent.
However, we all witnessed the kind of quality Butler has as a boxer. He is not on the level of Inoue and Casimero yet.
Its like Casimero was been sabotage for on that match that's why the fight between Butler and him has been off. If Casimero didn't get any problem on the restrictions on that fight for sure Butler cannot get those belt. And also maybe for that we see the fight between Inoue vs Casimero to happen. But that is past already and fans need to move on since Inoue vs Casimero will be listed on history as fans requested fight but never happen.
Now we since Inoue will fight Fulton we can still enjoy watching how Inoue could possibly dominate him and get another miles stone on his career.