Turns out, brainstorming is the worst thing you can do for ideation, and that includes any form of group ideating (e.g., "brainwriting"). Ideas comes from individual sweat and focus: Doing the hard research and thinking up the idea until the veins in your head burst. Brainstorming is usually the Hail Mary thrown when those steps haven't been owned by anyone. Mike and Jason just want ideas to come from the bottom of gin bottles.
The Havard Business Review article on solving brainstorming with brainwriting that kicked off this whole conversation.