the only thing that may add the edge is the knowledge that you have about the game you choose to play.
If that statement is directed toward gambling games then it's wrong because you don't get any edge over the house for any game that you play just because of the knowledge you have about it, that's now how gambling games work. I know there are a few games that might require your knowledge such as poker or blackjack, but even in those games, you need luck to be able to get good cards that you can use with your experience to win the games, but knowledge alone wouldn't make you win.
That statement can be correct about sports betting because it's the only part of gambling where your knowledge and experience are the most important things since you will need to have experience and knowledge about a sport and the teams involved to be able to make good predictions and get an edge over the sportsbook. Luck does play its role in sports betting as well but it's not completely dependent on that.
Casino games can be very uncertainty when it come to winning because the house have big chances of winning than us who are just a gambler. There may be some gamblers who make good profits from casino games but that do not happen to everyone. There would be people that would lose there funds nit because they are not intelligent or do not have a better skill but we all can not be a winner at the same time. There would be people that would lose their bet and their will also be those that would gain. We might be always lucky to be among people that do make consistent profits from betting and that do not mean that everyone is making reasonable profits from the same bets.