Great writeup. I've noticed the same thing by recording simultaneously with the watch workout app and strava on my iphone. The watch always says pace is slower.
1) Artificial scarcity - like Wordle or a NYTimes cover photo, there's only one per day. This focuses attention to one topic at a time.
2) Before/after polling. The audience is polled initially and then asked if they've changed their mind after a while reading arguments. The winner is the debate that changes the most minds.
Big fan of Intelligence Squared but haven't seen ChangeMyView before, thanks for sharing.
Regarding the polling suggestion, that's actually how it works! Clearly need to work on the messaging a bit, to make that more apparent. There's an initial poll and then you're asked if you've changed your mind after a minute of reading the arguments.