I'm sorry but it's just what the most competitive people are capable of doing. When you practice, you can compete at that speed and it isn't JUST about who read faster. The efficiency and cogency of arguments is STILL EVALUATED at that level.
You can make 20 arguments: 15 bad ones and 5 good ones. A fast and competent opponent will spend less than 5 seconds on each bad one (usually because it's been implicitly answered elsewhere or because it's been contradicted by a higher quality / more recent source) and however much time they need on the good ones.
Now, I agree with your characterization of the difference between 'fast' and 'slow' debate. Both are valuable, both emphasize their own skill sets. And yes, people without tons of time or resources will probably get more out of 'slow' debate. But as someone who did both, I think you're painting a caricature of 'fast' debate, which is an extremely rigorous activity filled with incredibly smart people.