If you've read any of the above posts, or even looked at some of the videos I've posted you'll noticed it's alive and well in Japan. It's a thriving over here in Japan.
Have you even raced 2 cell 21.5? Have you seen one going around the track in person?
They're pretty damn fast in my opinion.

I've raced 4.5 1 cell and the speed difference is not huge.
13.5 or even 17.5 is overkill for 2 cell, let alone running 1 cell.