Both have their strengths: one gives you constant dopamine hits, which can quickly lead to addiction. In sports, although betting may occur less frequently, the pleasure could be more intense, especially when you enjoy the sport you're betting on.
Perhaps for someone who pursues profits more, slot machines will be more affected because they can yield quick results. But for someone who enjoys sports more, they will surely get more pleasure. But not everyone is affected by betting in the same way. Some people are mentally stronger than others and tend to know how to control it.
Of course, casinos are more addictive for players because they are not tied to matches and bets are made very quickly. I think the faster the bets are made, the faster the player experiences emotional swings that throw him off balance, and this in turn can make him addicted. And sports betting is less provoking for players to make aggressive bets, everything is more calm and unhurried. Of course, this does not mean that you can't bet all your money and lose everything in one match, but I say on average among all players that bets are more stretched out in time, which has a better effect on players and their emotions.