@Gambio Maybe, but I'm not really seeing that. The only character clearly presented as evil in the tournament was the convict guy, and his backstory only explained his evil, it didn't seem to be intended to elicit total sympathy.
On the other hand, this guy wasn't presented as evil or even a jerk (unlike Adonis), maybe prideful at best, the flashback here was to show that Adonis was right in his evaluation.
He didn't truly love boxing. It was merely a duty forced upon him by his father.
I actually think one or two pages per flashback would actually remove a lot of the characterisation that makes the fights interesting. The point is not "this guy is evil we have to beat him".
This is a boxing manga not DBZ. The other boxers are all aiming at the title for their own reasons, and Cestus needs to overcome them. A prideful fighter who does not truly love boxing, who doesn't have the skill or determination to succeed will obviously fail at this. Explaining that fills out the story of the manga much better than "this guy is teh evulz".