Sweet Mask isn't the perfect hero. He's the perfect mercenary. The lack of empathy for ANYONE he goes against, even to his own comrades, definitely makes him some sort of sociopath. The way he doesn't want his "prefect" image broken by doing all his actual hero-ing without anyone watching. He has this sort of inflexible idea of what justice is and uses his position to threaten even higher ranking heroes into going along with his way. The petty fights he gets into with his allies actually HINDERS them when fighting in team battles which he just HAS to be on. His entitlement that the reason he stays at Rank A's Number 1 is to stop heroes who don't match up to his ideals from making S Class. A guy like him would a much better choice to become the next monster king than Garou, since this guy seems like he can throw away all his humanity at will if he gets to preserve his twisted ideology.