There can be a winner, but that person could be the winner because he’s right or just because he’s a better debater.
For example, professional creationists love to debate scientists. Why? Because the creationists are usually better debaters. They know they cannot convince people using the scientific evidence, so they choose debates instead.
As another example, I had a friend who was a champion debater in high school. They had their topics picked for them, and then the debaters had to gather whatever they could to support their side and debate it. So one time he might debate that motorcycle helmets should be required; another time he might be required to debate that they should not be required. Considering that he won almost all the time (I think he came in 2nd at the national level), he obviously could argue either side quite effectively (as a result, he ended up becoming an attorney). So it certainly wasn’t the facts that decided the winner; it was the debater.
With all of that said, it is possible to use debate to “win” somebody over. There have been cases here where somebody went into a debate with a strongly held position but came out of it with a changed mind because of the information that had been presented. It doesn’t happen often, but it does happen.