Just because one big project relies on emails does not mean they scale better. They work for the kernel because with that strong organization pretty much anything could work for the kernel.

Criticisms in the interview were essentially about low discipline that Github interface allows, and how they were not willing to adapt to the kernel needs, not about fundamental deficiencies of pull request based model.

So far nothing has been said about why pull requests via a website might handle less load than pull requests over email.