While there is not a winning strategy that you can apply to slots there are in fact a few games which can be beaten by the professionals, with one of them being sports bets.
Even if we reach the point in which casinos could perfectly price the odds of every single sport match around the world people cannot do that, which means that a lot of money could be gambled in favor of a team and then the casino will need to adjust the odds for that team winning in order to encourage people to bet on the opposite team, and as such professional gamblers can take the improved odds and give themselves a small edge this way, it is not easy to do but there are in fact some gamblers out there with a winning strategy on some gambling games.
Professional ones could do that, but it wouldn't be easy at all. I mean think about it, we are talking about sports here, if the sports world ever played by robots maybe you would be right, but even in like football manager type of games we are talking about random results even with the same tactics and roster.
So, we all know that in sports, there is never correct odds. If there were one, would have 1.00 for the team that will win, and x99999999999999999 for the one that will lose and we would know it for sure beforehand. Why do we have City vs Norwich game, the best ever EPL team and then the worst team, and the odds are not 1.01? That's because in football anything could happen, works for all sports.