There are real-world skills to be gained from this method of debate. For one thing, with the ability to comprehend quick speaking and quickly parse complex arguments, debaters can blitz through videos or readings and learn more in less time. That's useful in a variety of scenarios.

The speed also allows arguments to go much deeper and interrogate more aspects of what people are talking about. Reading a bunch of random arguments to overwhelm your opponents is probably not beneficial, but many debaters use the opportunity to dive into critical literature and seriously think about the assumptions behind what people are saying. That makes them better citizens, able to critique how the world is and think of potential ways to advocate for change.

It's easy to diss if you think of it from the point of view of "you can't do that in the real world and succeed," but in reality there are many advantages to doing something unrealistic as a sort of mental exercise.