What do you mean by "without flaws" and a "Mary Sue?" Vic wasn't a hero. He had little agency, even within the holodeck. He made a few big blunders, almost fumbling getting Kira and Odo together and not recognizing how the holodeck was starting to stunt Nog's recovery. Otherwise, he was just there to sing and give friendly advice.Vic Fontaine is one of the reasons why I really dislike the later seasons of DS9. How people love a character with absolute no flaws? He's the literal definition of a Mary Sue, every crew of DS9 loves Fontaine for no reason except that he's the most clever person on the universe, according to the writers at least.
I hate that musical episode, it's so bad it's unwatchable for me. The fact that I really hate traditional jazz, Las Vegas and Sinatra doesn't do me any favors.