> For example, if I asked you to code FizzBuzz while riding a unicycle, I'm pretty sure you would show more brain activity than if you were just sitting at a desk.

This is an astoundingly bad comparison and I think you know how invalid it is. Doing two separate unrelated activities at the same time is not the same as engaging more parts of your brain by focusing on a single task.

You’re right in that what works for one might not work for others, but your argument is dishonest at best.