so what;s wrong with a tried and tested system that we know works ?

There are definite design issues with a one tooth setup.

Nothing is centred, so either the large gear runs in an eliptical movement - meaning you need a much larger area than 200mm, or the tooth has to rotate within the outer gear, so that neeeds to be on an eliptical movement as well.
Eliptical movements do no transfer energy as efficiently as centred mechanisms.
It's also extremely weak.