Topaz was a unique character, as he was really neither hero or villain.
He actually saved the life of Yusuke Urameshi when his own team member tried to kill the Spirit Detective. Though, he vowed to kill Yusuke in the Dark Tournament.
His team did have some decent power to it.
But he was unlucky enough to go up against Toguro in the first match.
Where he single-handedly killed Topaz and his entire team without any significant injury to his own. What a bummer for them.